Computer Information System (old course)

A protocol is a set of rules and conventions that governs how data is formatted, sent, received and checked between devices on a network, for example TCP/IP, HTTP and FTP.

A computer virus is a malicious program that attaches itself to files or programs and spreads. It is harmful because it can:

• Delete, corrupt or steal data and programs
• Slow down the system and use up memory and disk space
• Cause crashes or stop the system from booting
• Spread to other computers through networks, email and removable disks
• Open the way for hackers to gain unauthorized access

Algorithm

1. Start.
2. Set $n = 95$.
3. While $n \ge 50$:
   • print $n$;
   • set $n = n - 5$.
4. Stop.

The loop prints 95, 90, 85, 80, 75, 70, 65, 60, 55, 50 (10 values) and stops when $n$ becomes 45.

Flowchart

 ( Start )
     |
 [ n = 95 ]
     |
 <-- n >= 50 ? --No--> ( Stop )
     |Yes
 /Print n/
     |
 [ n = n - 5 ]
     |
 (back to the test "n >= 50 ?")

Data processing is the series of operations (collecting, validating, sorting, calculating, storing, retrieving and presenting) performed on raw data to convert it into meaningful information.

Difference between sequential file processing and direct access file processing

The series is the powers of 2 from $2^0$ to $2^{10}$, each term being twice the previous one.

Algorithm

1. Start
2. Set $n = 1$
3. Display $n$
4. Set $n = n \times 2$
5. If $n \le 1024$, go to step 3
6. Stop

Tracing: the loop prints 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, and then $n$ becomes 2048 so the loop ends.

Flowchart (described step by step)

   [ Start ]
       |
   [ n = 1 ]
       |
       v
  < n <= 1024 ? > --No--> [ Stop ]
       |Yes
   /Display n/
       |
   [ n = n * 2 ]
       |
       +----> back to the decision

The decision diamond is tested before each display; the loop-back arrow returns to the diamond after n = n * 2.

A primary key is used to uniquely identify each record (row) in a table. It cannot be null or duplicated, and it is used to retrieve records quickly and to link tables through foreign keys.

Components of an expert system:

1. Knowledge base
2. Inference engine
3. User interface
4. Explanation facility
5. Knowledge acquisition facility

If cache misses are more frequent than cache hits, most data requests must be fetched from the slower main memory. The average memory access time increases and the overall system performance falls, so the cache is not effective.

The components of an expert system are:

1. Knowledge base
2. Inference engine
3. User interface
4. Explanation facility
5. Knowledge acquisition facility

1. Privacy: collection and use of personal data without the owner's consent.
2. Software piracy / intellectual property: copying or using software and content without a licence.
3. Computer crime and security: hacking, unauthorised access, and spreading viruses or fraud.

If cache hits are more than cache misses, the hit ratio is high. The CPU finds most data and instructions in the fast cache and rarely goes to the slower main memory. The average memory access time falls and the overall system performance improves.

RAM is called random access because any memory location can be read or written directly by its address, and the access time is the same for every location regardless of its position. Data does not have to be reached in sequence as it does on tape.

File processing is the way of creating, storing, accessing, updating and retrieving records in data files by programs. The method of access depends on how the records are organised on the storage medium.

Sequential file processing: records are stored and read one after another in a fixed order (usually sorted by a key). To reach a record, all previous records must be read first. Magnetic tape is a typical medium.

Direct (random) access file processing: any record can be accessed directly using its key or address without reading the earlier records. Magnetic disks are used.

Artificial Intelligence (AI) is the branch of computer science that makes machines and software perform tasks that normally need human intelligence, such as learning, reasoning, problem solving, understanding language and recognising images.

Expert system: an AI program that holds the knowledge of human experts in a particular field and uses it to give advice and solve problems like an expert. Examples are MYCIN (medical diagnosis) and DENDRAL (chemistry).

Components of an expert system

1. Knowledge base: stores the facts and rules (usually IF-THEN) gathered from experts.
2. Inference engine: the reasoning part that applies the rules to the facts to reach conclusions (forward or backward chaining).
3. User interface: lets the user ask questions and receive answers and advice.
4. Explanation facility: explains to the user how and why a conclusion was reached.
5. Knowledge acquisition facility: helps the knowledge engineer add or update knowledge in the knowledge base.
6. Working memory: holds the facts of the current problem.

RAM is called random access memory because any memory location can be reached directly in the same, constant time, whatever its position or the order of the previous access. The CPU need not read the earlier locations, unlike a tape where access is sequential.

A primary key is used to identify each record (row) in a table uniquely. Its values are unique and never null, so it prevents duplicate records, makes searching and sorting fast, and is used to link tables through foreign keys, which maintains data integrity.

• Privacy: unauthorised collection and use of personal information.
• Software piracy and copyright violation: illegal copying of software and content.
• Hacking and unauthorised access: breaking into systems and spreading viruses.

(Other examples are cyber bullying, plagiarism and the digital divide.)

Artificial Intelligence (AI) is the branch of computer science that builds machines and software able to perform tasks that normally need human intelligence, such as learning, reasoning, problem solving, understanding language and perception.

Expert system: An expert system is an AI program that stores the knowledge of human experts in a particular field and uses it to give advice or solve problems in that field, like a human specialist (e.g. medical diagnosis, loan approval, fault finding).

Components of an expert system

1. Knowledge base: Stores facts and rules (usually IF-THEN rules) collected from experts.
2. Inference engine: The reasoning part. It applies the rules to the facts using forward or backward chaining to reach conclusions.
3. User interface: Lets the user enter a problem and receive advice, often with questions and answers in simple language.
4. Explanation facility: Explains how and why the system reached a conclusion.
5. Knowledge acquisition facility: Helps the knowledge engineer add or update knowledge in the knowledge base.

Block diagram

Expert --> Knowledge Acquisition --> Knowledge Base
                                          |
User <--> User Interface <--> Inference Engine
                 |
         Explanation Facility

A cache hit ratio of 0.7 means that 70% of memory accesses by the CPU find the required data in the cache (hits), and the remaining 30% are misses that must be fetched from the slower main memory. A higher ratio gives faster average access time.

A laptop computer is a small, lightweight, portable personal computer with the display, keyboard, touchpad, speakers and battery built into a single unit. It can run on battery or mains power, so it can be used anywhere.

Computers are used because they process data with great speed, accuracy and reliability. They can store huge amounts of information, work continuously without fatigue, automate repetitive jobs, and help in communication, calculation, education, business, banking and entertainment, saving time, effort and cost.

A microphone is an input device that converts sound into electrical signals. Its uses include voice recording, voice chat and video conferencing, speech recognition and voice commands, singing and public address systems, broadcasting and podcasts, and online teaching.

Three input devices are the keyboard, the mouse and the scanner. Others include the microphone, webcam and joystick.

A plasma display is a flat-panel display in which each pixel is a tiny cell filled with ionised gas (plasma, usually neon and xenon). When a voltage is applied the gas emits ultraviolet light that makes phosphors glow red, green or blue. It gives bright images and wide viewing angles and is used in large televisions.

A spreadsheet (for example Microsoft Excel) is used to enter, store, calculate, analyse and present numerical data in rows and columns. It is used for accounting, budgeting, payroll, statistics, financial analysis, tables and charts, using formulas and functions that recalculate automatically.

Three storage devices are the hard disk, the pen drive (USB flash drive) and the CD/DVD. Others include magnetic tape and memory cards.

A client-side scripting language (such as JavaScript) runs in the user's web browser. Its benefits are:

• Faster response, because no round trip to the server is needed for each action.
• Reduced server load and network traffic.
• Immediate validation of form input.
• Interactive and dynamic pages (menus, animations, effects).
• Works with offline or already loaded page content.

Image quality is the degree to which a digital image looks clear, sharp and true to the original. It depends on resolution (number of pixels), colour depth (bits per pixel), compression, brightness and contrast, and noise. Higher resolution and colour depth give better quality but larger file size.

Why memory hierarchy is maintained

No single memory is at once very fast, large and cheap. Fast memory (registers, cache) is expensive and small, whereas slow memory (hard disk) is cheap and large. A hierarchy arranges them as registers, cache, main memory (RAM), then secondary storage. Frequently used data is kept in the faster upper levels, and the rest in lower levels, so the average access time is close to that of the fast memory while the overall cost per bit stays low and the capacity stays large. It works because of the principle of locality of reference.

Address register size

$4\text{ GB} = 4 \times 2^{30}\text{ bytes} = 2^{2}\times 2^{30} = 2^{32}\text{ bytes}$

For byte-addressable memory, the number of address bits needed is $\log_2 2^{32} = 32$.

So the address register must be 32 bits wide. A 64-bit architecture's registers are larger, but only 32 bits are needed to address 4 GB.

Row $i$ (for $i = 1$ to $5$) prints the numbers from 5 down to $i$: row 1 prints 5 4 3 2 1 and row 5 prints 5.

Algorithm

1. Start.
2. Set i = 1.
3. Repeat steps 4 to 8 while i <= 5.
4. Set j = 5.
5. Repeat steps 6 and 7 while j >= i.
6. Print j followed by a space.
7. Set j = j - 1.
8. Go to a new line, set i = i + 1.
9. Stop.

Check: for i = 1, $j$ runs 5 to 1 giving 5 4 3 2 1; for i = 5, $j$ runs 5 to 5 giving 5. This matches the required pattern.

C code

#include <stdio.h>
int main() {
    int i, j;
    for (i = 1; i <= 5; i++) {
        for (j = 5; j >= i; j--)
            printf("%d ", j);
        printf("\n");
    }
    return 0;
}

A database is an organised collection of related data stored so that it can be easily accessed, managed and updated, usually through a database management system (DBMS).

Advantages

1. Reduced data redundancy and inconsistency. Data is stored centrally once instead of in many files, so duplication is minimal and updates stay consistent.
2. Data sharing and integrity. Many users and applications can use the same data at the same time, and integrity constraints keep it accurate.
3. Security and backup. Access rights and passwords control who can view or change data, and the DBMS supports backup and recovery.

Other advantages include data independence, faster retrieval with queries, and standardisation.

Remote login is the facility of connecting to and using a computer located at another place over a network, as if the user were sitting at it, using programs such as Telnet, SSH or remote desktop. The user's own machine acts as a terminal and the commands run on the remote machine.

Situations where it is used

• An administrator maintains or troubleshoots a server from a distance.
• Employees access office files and applications from home.
• Technical support fixes a customer's computer.
• Using a powerful remote computer or database that is not available locally.
• Managing network devices such as routers and switches.

Malicious programs (malware) include viruses, worms, trojans, spyware and ransomware.

Reasons for infection

• Opening e-mail attachments or links from unknown senders (phishing).
• Downloading pirated software, games or files from unsafe sites.
• Using infected pen drives or other removable media.
• Having no antivirus, or an outdated one, and not updating the operating system.
• Weak passwords and open network connections.
• Visiting malicious websites and clicking pop-up advertisements.

Solutions

• Install reputable antivirus and anti-spyware software and keep it updated; scan regularly, including pen drives.
• Apply operating system and software patches.
• Use a firewall.
• Avoid unknown attachments, links and pirated software.
• Take regular backups so that data can be restored.
• Use strong passwords and limited user rights.
• Educate users about safe computing.

Software documentation is the written description of a software system: what it does, how it is designed, and how to use and maintain it. A software system must be documented for these reasons.

• Understanding and communication. It gives analysts, designers, programmers, testers and users a common reference to the requirements and design.
• Maintenance and modification. Programmers who did not write the code can understand and change it; this is the most costly phase of the life cycle.
• User support. User manuals, help files and training guides teach users to operate the system correctly.
• Continuity. When team members leave, knowledge is not lost.
• Testing and quality control. Test plans and specifications show what to verify and permit audit and standards compliance.
• Reuse and legal protection. It helps reuse of modules and serves as a record for contracts and acceptance.

Types: system (technical) documentation including requirement specification, design, program listings and test results; and user documentation including user manual, operations manual and installation guide.

Primary storage devices (RAM, ROM, cache) are built from semiconductor chips with millions of transistors, which are costly to manufacture. They are directly accessed by the CPU at very high speed, so they need fast, complex technology and the cost per bit is far higher than for magnetic or optical secondary storage. This is why they are kept small in capacity.

A device driver is a small system software program that lets the operating system communicate with and control a hardware device, such as a printer, scanner or graphics card, by translating general OS commands into the device's specific instructions.

Factors to consider when purchasing a PC:

• Purpose of use (office, gaming, design, programming).
• Processor type and speed, RAM size and hard disk capacity.
• Budget and price.
• Brand, warranty and after-sales service.
• Display, ports, graphics and expandability or upgrade options.
• Software compatibility and operating system.
• Power consumption and portability (desktop or laptop).

A computer understands only machine language (binary 0s and 1s), whereas people write programs in assembly or high-level languages that are easier to read. A language translator (assembler, compiler or interpreter) converts these programs into machine code so the computer can execute them.

A scripting language is a programming language, usually interpreted rather than compiled, used to write short programs (scripts) that automate tasks or control other applications. Examples are JavaScript, PHP, Python, VBScript and shell scripts, widely used in web development.

Common flowchart symbols:

• Oval (terminator): start and end.
• Parallelogram: input and output.
• Rectangle: process or calculation.
• Diamond: decision (yes/no condition).
• Arrows (flow lines): direction of flow.
• Circle: connector (on the same page).
• Off-page connector: link to another page.
• Hexagon: preparation or loop initialisation.

Conversion strategies in system implementation:

1. Direct (abrupt) conversion. The old system is replaced by the new one at once.
2. Parallel conversion. Both systems run together for a period.
3. Phased conversion. The new system is introduced module by module.
4. Pilot conversion. The new system is first tried in one location or department.

A data warehouse is a large central repository of integrated, subject-oriented, time-variant and non-volatile data collected from many sources, stored to support analysis, reporting and decision making rather than daily transactions.

Animation is a sequence of artificially created images (drawn or computer-generated) shown rapidly to give an impression of movement. Video is a sequence of frames recorded from real-life scenes with a camera. Animation is built frame by frame by the designer and usually has smaller file size, while video captures real motion and typically needs more storage.

TCP/IP (Transmission Control Protocol / Internet Protocol) is the essential protocol suite. IP addresses and routes packets, and TCP ensures reliable delivery, so computers of different types can communicate over a network or the Internet.

A web browser is application software used to access, retrieve and display web pages and other content on the World Wide Web using URLs and the HTTP protocol. Examples are Google Chrome, Mozilla Firefox, Microsoft Edge and Safari.

Communication media are of two types.

Guided (wired) media

• Twisted pair cable (telephone lines, LAN cable)
• Coaxial cable (cable TV)
• Optical fibre cable (high-speed Internet)

Unguided (wireless) media

• Radio waves (FM radio, Wi-Fi)
• Microwave (mobile towers)
• Satellite (TV broadcasting, GPS)
• Infrared (TV remote)

Symbols in an E-R diagram:

• Rectangle: entity.
• Double rectangle: weak entity.
• Ellipse (oval): attribute.
• Double ellipse: multivalued attribute.
• Dashed ellipse: derived attribute.
• Underlined text in ellipse: key attribute.
• Diamond: relationship.
• Double diamond: identifying relationship of a weak entity.
• Lines: connections between entities, relationships and attributes.

A neural network is a computing model inspired by the human brain, made of many interconnected processing units (artificial neurons) arranged in layers, which learns patterns from data by adjusting connection weights. It is used for recognition, prediction and classification tasks.

Data processing is the series of operations performed on raw data to convert it into meaningful, useful information.

Three phases

1. Input. Data is collected, verified and entered into the computer (for example marks of students typed in).
2. Processing. The CPU performs operations on the data such as sorting, classifying, calculating, comparing and summarising (for example total and percentage).
3. Output. The results are presented as information in the form of reports, charts or displays, and may be stored for later use (for example mark sheets).

A system is a set of interrelated components that work together toward a common goal by accepting inputs and producing outputs.

The longest (and most costly) phase of the SDLC is maintenance, which begins after the system is installed and continues throughout its useful life. It involves:

• Corrective maintenance: fixing errors found in use.
• Adaptive maintenance: modifying the system for changes in the environment, law or hardware.
• Perfective maintenance: improving performance or adding new features requested by users.
• Preventive maintenance: changes made to avoid future problems.

It is long because the system must keep working for many years, and the needs of users and the business keep changing.

Structured programming is a programming approach that builds a program from a small set of control structures (sequence, selection and iteration) and divides it into modules or functions, avoiding unrestricted use of goto. The approach is top-down, giving clear, easily tested and maintained code. Examples are C and Pascal.

Difference from object-oriented programming (OOP)

An expert system is an artificial intelligence program that stores the knowledge of human experts in a particular field and uses it to solve problems and give advice in that field, as a human expert would.

Main components

• Knowledge base: facts and IF-THEN rules collected from experts.
• Inference engine: applies the rules to the known facts to reach conclusions.
• User interface: lets the user put questions and see the advice and the reasoning.

Examples: MYCIN (medical diagnosis), DENDRAL (chemical analysis) and systems for loan approval or fault diagnosis.

Advantages: it is available at all times, gives consistent answers and keeps scarce expertise from being lost.

Software is a set of programs, procedures and related data that instructs the hardware what to do and how to do it. It cannot be touched, unlike hardware.

Algorithm (smallest of N numbers)

1. Start.
2. Read $N$, the count of numbers.
3. Read the first number and set $small = A_1$.
4. Set $i = 2$.
5. While $i \le N$:
   • read $A_i$;
   • if $A_i < small$, set $small = A_i$;
   • set $i = i + 1$.
6. Print $small$.
7. Stop.

Flowchart (described in order of symbols)

 ( Start )
     |
 /Read N, A1/
     |
 [ small = A1 ; i = 2 ]
     |
 <-- i <= N ? ----No----> /Print small/ --> ( Stop )
     |Yes
 /Read Ai/
     |
 < Ai < small ? > --Yes--> [ small = Ai ]
     |No                        |
     +------------<-------------+
     |
 [ i = i + 1 ]  --> back to the test "i <= N ?"

Example: for 7, 3, 9, 2, 5 the value of $small$ goes 7, 3, 3, 2, 2, so the output is 2.

A firewall is a hardware or software system placed between a trusted private network and an untrusted network such as the Internet. It filters incoming and outgoing traffic according to security rules and blocks unauthorised access.

Securing data

• Keep regular backups and store them safely.
• Use access control (user names, passwords, permissions) and encrypt sensitive data.
• Use antivirus software and keep the system updated.

Securing messages

• Encrypt messages (for example with SSL/TLS, PGP or secure e-mail).
• Use digital signatures to prove who sent a message and that it was not altered.
• Use secure protocols such as HTTPS and SFTP.

Securing the network

• Install a firewall and an intrusion detection system.
• Use strong authentication and change passwords regularly.
• Use VPNs for remote access, secure Wi-Fi with WPA2 and disable unused ports and services.
• Apply security patches and monitor traffic.

System software is the set of programs that controls and manages the computer hardware and provides a platform on which application software runs. Examples are the operating system, language translators and device drivers.

A CRT monitor is bulky, heavy and uses high power and high voltage. A laptop must be thin, light and battery-operated, so it uses flat LCD or LED screens instead.

The smallest memory is the register inside the CPU. It holds the data, instruction or address that the CPU is working on at that moment, so the CPU can access it at the highest speed.

The CPU understands only machine language (binary). An assembler is required to translate assembly language programs, written with mnemonics such as ADD and MOV, into machine code so that the computer can execute them.

A machine dependent language is a language whose instructions are designed for a particular type of computer or processor, so a program written in it works only on that machine. Machine language and assembly language are examples.

1. Problem or requirement analysis (preliminary investigation)
2. System design
3. Coding (implementation)
4. Testing
5. Installation (deployment)
6. Maintenance

Networking is required to share resources such as printers, files, data and software, to communicate quickly (e-mail, chat), to give central control and backup of data, and to reduce cost by sharing expensive hardware.

Optical fiber is a thin strand of glass or plastic that carries data as pulses of light. It gives very high bandwidth and speed, low signal loss over long distances, and is free from electromagnetic interference.

HTTP (Hypertext Transfer Protocol) is used to request and transfer web pages between a browser and a web server. FTP (File Transfer Protocol) is used to upload and download files between computers, normally after logging in, and it keeps separate control and data connections.

Multimedia is the combined use of different media such as text, graphics, images, audio, video and animation in one computer-based presentation or application, usually with user interaction.

Data processing is the series of operations (collecting, sorting, calculating, storing and presenting) that converts raw data into meaningful information.

Artificial intelligence (AI) is the branch of computer science that makes machines perform tasks that normally need human intelligence, such as learning, reasoning, problem solving and understanding language.

Message security on the Internet is achieved by encryption (converting a message into unreadable cipher text with a key), digital signatures to prove the sender and detect alteration, and secure protocols such as SSL/TLS and HTTPS.

Spyware is malicious software that installs itself secretly on a computer and collects information such as browsing habits, passwords and bank details, and sends it to another person without the user's knowledge.

• Hacking (unauthorised access to computer systems)
• Spreading viruses, worms and other malware
• Online fraud and credit card theft
• Software piracy and copyright violation

Network topology is the physical or logical layout of the nodes (computers and devices) and the links connecting them in a network. Common topologies are bus, star, ring, mesh and tree.

Star topology

In a star topology every node is connected by its own cable to a central device, the hub or switch. All data passes through this central device.

• Advantages: failure of one cable or node does not affect the others; easy to add or remove nodes; easy to find faults and manage.
• Disadvantages: if the central hub fails the whole network stops; it needs more cable than a bus; the hub adds cost.

• Speed: a computer performs millions or billions of operations per second.
• Accuracy: results are correct as long as the input and program are correct; errors usually come from wrong data (GIGO).
• Diligence: it can work for long hours without tiredness or loss of concentration.
• Versatility: it can do many kinds of work, such as calculation, drawing, communication and entertainment.
• Storage: it can store large amounts of data and recall it when needed.
• Automation: once a program is started, it carries out the tasks by itself.
• No intelligence (IQ): it does only what it is told and cannot decide by itself.

A bus is a set of parallel wires or lines that carries data, addresses and control signals between the CPU, memory and I/O devices inside a computer.

Types of bus

• Data bus: carries data between the CPU, memory and I/O devices. It is bidirectional, and its width (8, 16, 32, 64 bits) decides how much data moves at one time.
• Address bus: carries the address of the memory location or I/O device the CPU wants to access. It is unidirectional (from the CPU), and its width decides the maximum memory that can be addressed ($2^n$ locations for $n$ lines).
• Control bus: carries control and timing signals such as read, write, interrupt and clock to coordinate all the operations. It is bidirectional.

• Database management system (DBMS): software that is used to create, store, organise, retrieve and control a database and to give users controlled access to it. Examples are MS Access, MySQL and Oracle.
• Data mining: the process of analysing large amounts of data to discover hidden patterns, relationships and useful knowledge, using statistics and artificial intelligence techniques.
• Data warehouse: a large central store of integrated, subject-oriented and historical data collected from many sources, kept for analysis and decision making rather than daily transactions.

Functions

• RAM: the main working memory. It temporarily holds the programs and data being used by the CPU. It is volatile, so its content is lost when power goes off.
• ROM: permanent, non-volatile memory that holds start-up programs such as the BIOS or boot instructions. Its content is normally only read.
• Cache memory: a very fast, small memory between the CPU and RAM that keeps frequently used data and instructions, so the CPU waits less.

Types of RAM

• SRAM (static RAM): uses flip-flops, is fast and costly, needs no refreshing and is used for cache.
• DRAM (dynamic RAM): uses capacitors, is cheaper and slower, and needs constant refreshing. It is used as main memory.
• SDRAM: DRAM synchronised with the system clock for higher speed. DDR SDRAM is a faster version that transfers data on both clock edges.

Image quality is the degree of clarity and detail of an image. It depends on the resolution (number of pixels), colour depth (bits per pixel), sharpness and the amount of compression used.

Image file format is the way in which the image data is organised and stored in a file, usually with the type of compression. It is shown by the file extension.

TIFF (Tagged Image File Format, .tif)

• Stores images without loss (lossless or uncompressed) in high quality with many colours.
• Used in printing, publishing and scanning.
• File size is large, and it is not suitable for web pages.

JPEG (Joint Photographic Experts Group, .jpg)

• Uses lossy compression, so file size is small, but some quality is lost with more compression.
• Supports about 16.7 million colours (24-bit).
• Best for photographs and web use; it is poor for sharp lines and text, and does not support transparency.

GIF (Graphics Interchange Format, .gif)

• Supports only 256 colours (8-bit) with lossless compression.
• Supports transparency and simple animation.
• Best for logos, line drawings, icons and simple graphics; it is not suitable for photographs.

1. Speed
2. Accuracy
3. Diligence (no tiredness)
4. Versatility
5. Large storage capacity

Battery-backed RAM, that is CMOS RAM / NVRAM (non-volatile RAM), is a RAM that keeps its content when the main power is off because a small battery or a flash memory supplies it.

A programming language is required to write instructions in a form that humans can understand and the computer can be made to execute, so we can tell the computer what to do and build software.

Fast memory is expensive and small, while large memory is cheap and slow. A memory hierarchy (registers, cache, RAM, secondary storage) gives a good balance of speed, cost and capacity, so the CPU gets the speed of fast memory and the size of cheap memory.

Firmware is software permanently stored in hardware, usually in ROM or flash memory, that controls how the device works, for example the BIOS of a computer or the program in a router.

A computer can execute only machine language. A language translator (assembler, compiler or interpreter) is required to convert programs written in assembly or high-level languages into machine language.

The purpose of the testing phase is to run the system with test data to find and remove errors, and to check that it meets the user's requirements and works correctly before it is put to use.

Hypertext is text that contains links (hyperlinks) to other text or documents, so that a reader can jump from one page to another by clicking. It is the basis of the World Wide Web.

GIF is preferred. It uses lossless compression with a limited number of colours, so the edges of lines and text stay sharp and the file is small, while JPEG's lossy compression blurs lines and text.

Logical network topology describes how data actually flows between the nodes of a network (for example Ethernet bus or token ring), regardless of the physical arrangement of cables and devices.

1. It allows a user to log in to and control a remote computer from his or her own computer, as if sitting at it.
2. It lets users use remote programs and resources without being physically present, so there is no need to travel.

• Entity: rectangle, with the entity name inside.
• Relationship: diamond, with the relationship name inside.
• Attribute: ellipse (oval), with the attribute name inside.

 +---------+       /\          ( attribute )
 | Entity  |      /  \
 +---------+      \  /
                   \/
               Relationship

A firewall is used to protect an organisation's internal network from unauthorised access, hackers and malicious traffic from the Internet, and to control which traffic is allowed in or out according to security rules.

Layers used in a neural network:

1. Input layer: receives the raw input features.
2. Hidden layer(s): one or more layers that process the inputs using weights and activation functions.
3. Output layer: produces the final result (prediction or classification).

System software is the set of programs that controls and manages the hardware and provides a platform for running other software, e.g. operating system, device drivers, language translators.

Utility software is system software that performs maintenance and support tasks, e.g. disk defragmenter, antivirus, backup and file compression tools.

Application software is software designed to perform a specific task for the user, e.g. word processors, spreadsheets, Photoshop.

Classification

Both compilers and interpreters are language translators that convert a high-level language program into machine language.

Similarities

• Both translate high-level source code into machine-understandable form.
• Both detect syntax errors in the source program.
• Both are system software and are specific to a programming language.

Differences

An expert system is an artificial intelligence program that stores the knowledge of human experts in a specific field and uses it to give advice or solve problems the way an expert would, e.g. medical diagnosis systems.

Components of an expert system

1. Knowledge base: stores facts and rules (usually IF-THEN rules) collected from human experts.
2. Inference engine: the reasoning part; it applies the rules of the knowledge base to the facts to derive conclusions (forward or backward chaining).
3. User interface: lets the user enter questions or data and see the advice, usually in natural-like language or menus.
4. Explanation facility: explains how and why the system reached a conclusion.
5. Knowledge acquisition facility: helps the knowledge engineer add or update knowledge in the knowledge base.

A network is a collection of computers and other devices connected by communication media so that they can share data, hardware and software resources.

LAN vs WAN

The System Development Life Cycle (SDLC) is a structured, step-by-step process followed to plan, create, test and deploy an information system.

Phases of SDLC

1. Preliminary investigation / problem identification: the problem is defined and a feasibility study (technical, economic, operational) is carried out to decide whether to proceed.
2. System analysis: the existing system is studied through interviews, questionnaires and observation; user requirements are gathered and tools such as DFD and decision tables are used to document them.
3. System design: the new system is designed, including inputs, outputs, files, database, processing logic and the user interface.
4. System development (coding): programmers write the programs from the design; tools such as CASE may be used; technical and user documents are prepared.
5. System testing: units, modules and the whole system are tested with test data to find and remove errors.
6. Implementation / conversion: the new system is installed and users are trained; conversion may be direct, parallel, phased or pilot.
7. Maintenance and review: errors are corrected, changes are made and the system is improved as needs change, until a new SDLC starts.

Factors that determine the processing power of a computer:

• Clock speed of the processor (GHz)
• Word size (bus width) of the CPU
• Number of cores
• Size and speed of RAM
• Size of cache memory
• Speed of the system bus and storage devices

A presentation tool (e.g. MS PowerPoint) is used to create slides combining text, images, charts, audio and video so that information can be presented to an audience in a clear, attractive and organized way.

An operating system is used to manage the computer's hardware and software resources and to act as an interface between the user and the hardware. It manages the processor, memory, files and input/output devices, runs application programs, and makes the computer convenient and efficient to use. Without it, the user would have to control hardware directly in machine language.

A high-level language program must first be translated into machine language by a compiler or interpreter. This translation takes extra time (and with an interpreter it is repeated at every statement on every run), and the generated machine code is usually less optimized than hand-written low-level code. Hence execution is slower than with a low-level language.

Iteration is the repeated execution of a set of statements until a given condition is satisfied (looping).

Example: printing the numbers 1 to 5 in C:

for (int i = 1; i <= 5; i++)
    printf("%d ", i);

The statement printf is executed five times, giving 1 2 3 4 5.

They are created in the system analysis phase, where the existing system is studied and the requirements are documented (some designs also refine them in the system design phase).

The quality of an image depends on:

• Resolution (number of pixels)
• Color depth (bits per pixel)
• Image size
• File format and compression used
• Quality of the capturing device and display device

The seven layers of the OSI reference model (from top to bottom):

1. Application layer
2. Presentation layer
3. Session layer
4. Transport layer
5. Network layer
6. Data link layer
7. Physical layer

It is a website address (domain name):

• www: World Wide Web, the service used
• fomecd: the name of the organization or site
• edu: educational institution (domain type)
• np: Nepal (country code)

FTP (File Transfer Protocol) is used to upload files to and download files from a remote computer or server over a network such as the Internet.

An IP address is assigned to a computer to give it a unique identity in the network, so that data packets can be addressed to it and routed correctly between the sender and receiver.

Memory hierarchy is the arrangement of the different types of memory of a computer in levels according to speed, cost and capacity. Going down the hierarchy, speed and cost per bit decrease while capacity increases.

          /\
         /Reg\          Registers      (fastest, smallest, costliest)
        /------\
       / Cache  \       Cache memory
      /----------\
     / Main (RAM) \     Main memory
    /--------------\
   / Secondary (HDD) \  Magnetic disk, SSD
  /------------------\
 / Tertiary (tape/CD) \ Optical disk, magnetic tape (slowest, largest, cheapest)

The CPU accesses the upper levels most quickly, so frequently used data is kept in them; the lower levels hold large amounts of data permanently.

NVRAM (Non-Volatile RAM) is random access memory that retains its contents even when power is switched off. It is usually a SRAM backed by a battery, or flash memory, and is used to store settings such as BIOS/CMOS configuration data and in devices such as routers and SSD-type storage.

A language translator is a program that converts a program written in a high-level language or assembly language into machine language so that the computer can execute it. The types are assembler, compiler and interpreter.

Scripting language vs object-oriented language

Three applications of AI

1. Expert systems, e.g. medical diagnosis and fault finding.
2. Robotics, e.g. industrial robots that perform tasks automatically.
3. Natural language processing and speech recognition, e.g. voice assistants and machine translation.

(Others: computer vision, game playing, machine learning.)

Neural network: an artificial neural network is a computing model inspired by the human brain. It consists of many interconnected processing units (neurons) arranged in an input layer, hidden layer(s) and an output layer. Each connection has a weight, and the network learns by adjusting these weights from training examples. It is used for pattern recognition, classification and prediction.

The system development phase of SDLC is the phase in which the system is actually built: programmers write the code according to the design specifications, the hardware and software are acquired and installed, the programs are tested, and documentation is prepared.

Technical document vs user document

A network is a group of two or more computers and devices connected by communication media to share data and resources.

Types of network (by geographical area)

1. LAN (Local Area Network): covers a small area such as a room, building or campus. It is fast, cheap and privately owned, e.g. a school computer lab.
2. MAN (Metropolitan Area Network): covers a city or large town and connects several LANs, e.g. a cable TV network or a bank's branches in a city.
3. WAN (Wide Area Network): covers a large area such as a country or continent using telephone lines, satellites or fibre; it is slower and costlier, e.g. the Internet.

(A PAN, personal area network, covers a few metres around one person, e.g. Bluetooth devices.)

(a) The Internet is a worldwide network of interconnected computer networks that use the TCP/IP protocol to exchange information. It provides services such as the WWW, email, FTP and chat.

Static web page: a page whose content is fixed and is the same for every visitor until the author edits the file. It is written in HTML/CSS and is delivered as stored. Example: an "About us" or contact page.

Dynamic web page: a page whose content is generated at the time of request by server-side or client-side scripts, often from a database, so it can differ for each user or time. Example: a Facebook news feed, an online shopping cart, a result-checking page (PHP, ASP, JSP).

(b) An image file format is a standard way of storing a digital image in a file, specifying how the pixel data is encoded and compressed (e.g. JPEG, GIF, PNG, BMP).

Algorithm

1. Start
2. Read the number $n$
3. Set $num = n$, $rev = 0$
4. While $num > 0$: set $digit = num \bmod 10$, $rev = rev \times 10 + digit$, $num = \lfloor num/10 \rfloor$
5. If $rev = n$, display "Same as the original number"; otherwise display "Not the same"
6. Display $rev$
7. Stop

Example: $n = 121$ gives $rev = 1, 12, 121$, so $rev = n$ (same). For $n = 123$, $rev = 321 \ne 123$ (not same).

Flowchart (described step by step)

   [ Start ]
       |
  /Read n/
       |
  [ num = n, rev = 0 ]
       |
       v
  < num > 0 ? > --No--> < rev == n ? > --Yes--> /Print "Same"/ --+
       |Yes                    |No                               |
  [ digit = num % 10 ]    /Print "Not same"/ ------------------>-+
  [ rev = rev*10 + digit ]                                       |
  [ num = num / 10 ]                                      /Print rev/
       |                                                         |
       +--> back to  num > 0 ?                              [ Stop ]

Factors to consider when purchasing a computer:

• Purpose of use
• Processor type and speed
• RAM size
• Storage capacity and type (HDD/SSD)
• Display and graphics quality
• Price and budget
• Brand, warranty and after-sales service
• Compatibility, upgradability and available software

A register set is required in the CPU to hold instructions, addresses, data and intermediate results temporarily while the program executes. Registers are the fastest storage, so the CPU can access this data without waiting for the slower main memory, which makes processing fast.

Common flowchart symbols:

 (  Terminal  )     /  Input/Output  /     [  Process  ]     <  Decision  >     ( ) Connector

A compiler translates the whole program into machine code at once and produces an object file that executes fast, and it reports all errors after compilation. An interpreter translates and executes the program one statement at a time without producing an object file, so it is slower and stops at the first error.

• JPEG supports millions of colors; GIF supports only 256 colors.
• JPEG uses lossy compression; GIF uses lossless compression.
• JPEG is best for photographs; GIF is best for simple graphics and logos.
• GIF supports animation and transparency; JPEG does not.

CASE tools are used for developing prototypes in the system design phase (they also help in analysis and development).

• Phased conversion: the new system is introduced in stages, one module or function at a time, until the whole old system is replaced.
• Pilot conversion: the complete new system is first installed and tried in only one location or department (the pilot site); after it works well, it is introduced to the other locations.

A resource is any hardware, software or data component that can be used or shared in a computer system or network, e.g. CPU, memory, printer, files and storage.

A communication satellite is an artificial satellite placed in orbit around the Earth that receives signals from an earth station (uplink), amplifies them and retransmits them to another earth station (downlink). It is used for TV broadcasting, telephone, Internet and long-distance data communication.

The relations give two entities, Worker and Department, joined by the relationship Belongs to. Each worker belongs to one department, and a department can have many workers, so the relationship is many-to-one (N:1).

 [ Worker ]                                   [ Department ]
 (Worker_ID)  (WName) (WAddress)      (DepartmentID) (Name)
      \                                        /
       \---N---<  Belongs to  >---1----------/

• Entity Worker: attributes Worker_ID (primary key, underlined), WName, WAddress.
• Entity Department: attributes DepartmentID (primary key, underlined), Name.
• Relationship Belongs to: a rectangle-diamond between the two entities (diamond for the relationship, rectangles for entities, ovals for attributes). In the relational form it holds the keys Worker_ID and DepartmentID, which are foreign keys referring to Worker and Department.

Anti-piracy means the laws, technical measures and practices used to prevent the illegal copying, distribution and use of copyrighted software, music, films and other digital content. Examples are licence keys, product activation, watermarking and copyright enforcement.

Applications of AI: expert systems (medical diagnosis), natural language processing and speech recognition, robotics, computer vision and face recognition, game playing (e.g. chess), machine translation, and intelligent tutoring or decision support systems.

Genetic Algorithm: a search and optimisation technique based on natural selection and genetics. It starts with a population of candidate solutions (chromosomes). Each is evaluated by a fitness function. The fitter ones are selected to reproduce using crossover and mutation, producing a new generation. This repeats until a good enough solution is found.

FTP (File Transfer Protocol): a protocol for uploading and downloading files between a client and a server over a network. It uses separate control and data connections and usually needs a username and password.

HTTP (HyperText Transfer Protocol): the application-level protocol used by web browsers and web servers to request and transfer web pages and other resources. The browser sends a request and the server returns a response. HTTPS is its secure version.

Search engine: a program or website that searches an index of web pages for the keywords a user enters and lists the matching results in ranked order, e.g. Google and Bing. It works by crawling, indexing and ranking.

Computer network: a collection of two or more computers and other devices connected by communication media so that they can share data, hardware and software resources.

Data communication: the exchange of digital data such as text, files, images and video between devices over a transmission medium. It needs a sender, a receiver, a message, a medium and a protocol, e.g. email and file transfer.

Voice communication: the transmission of human speech between people over a network, either as analogue signals on traditional telephone lines or as digital packets in VoIP, mobile calls and video conferencing. It is real-time and needs low delay.

Difference

Steps in sequential (batch) processing

1. Collect transactions and store them in a transaction file.
2. Sort the transaction file into the same key order as the master file.
3. Read a record from the transaction file and the master file and compare keys.
4. If the keys match, update the master record; if they do not, copy the master record unchanged.
5. Write the result to the new master file, and repeat until end of file.
6. Produce reports.

Steps in direct-access processing

1. Input the transaction (with its key).
2. Apply an address calculation (hashing) or index lookup to find the record location.
3. Read that record directly from the disk.
4. Update or process it.
5. Write the record back to the same location and give the output immediately.

Let the four marks be m1, m2, m3, m4, each out of 100, so the percentage is the total divided by 4.

1. Start
2. Read m1, m2, m3, m4
3. Set total = m1 + m2 + m3 + m4
4. Set percentage = total / 4
5. If percentage >= 85, grade = A and go to step 11
6. Else if percentage >= 70, grade = B and go to step 11
7. Else if percentage >= 55, grade = C and go to step 11
8. Else if percentage >= 45, grade = D and go to step 11
9. Else if percentage >= 32, grade = E and go to step 11
10. Else grade = F
11. Print percentage and grade
12. Stop

For example, marks 80, 70, 60, 50 give a total of 260 and a percentage of $260/4 = 65$, which is grade C (at least 55 and below 70).

Disadvantages of a plasma display:

1. Consumes more power and produces more heat than LCD or LED.
2. Heavy and bulky.
3. Screen burn-in (image retention) can occur.
4. Expensive, and works less well at high altitude.
5. Shorter life and reflective screen glare.

The three basic control structures (operations) used in an algorithm are:

1. Sequence (statements executed one after another)
2. Selection or decision (if-else, branching)
3. Iteration or repetition (loops)

They are created in the implementation (development and implementation) phase of the SDLC, when the system is built, tested and delivered. The user manual and the technical documentation are prepared then, for training and later maintenance.

System analysts are IT professionals who study an organisation's existing system and its business needs, then analyse, design and help implement an information system to meet them. They act as a bridge between users and programmers.

Animation is the technique of creating the illusion of movement by displaying a rapid sequence of still images or frames, each slightly different from the one before, e.g. 24 or more frames per second.

The layers of the TCP/IP model are:

1. Application layer
2. Transport layer
3. Internet (network) layer
4. Network access layer (the data link and physical layers)

The Domain Name System (DNS) translates human-friendly domain names such as www.example.com into numerical IP addresses that computers use to find each other. Users therefore do not have to remember IP addresses to reach a website.

The relations give two entities, Teacher and Student, joined by the relationship Supervise. A teacher can supervise many students and a student can be supervised by many teachers, so the relationship is many-to-many (M:N).

 [ Teacher ]                                [ Student ]
 (Teacher_id) (First_Name)           (Student_id) (First_Name)
 (Last_Name)                         (Last_Name)
      \                                     /
       \---M---<  Supervise  >---N--------/

• Entity Teacher: Teacher_id (primary key, underlined), First_Name, Last_Name.
• Entity Student: Student_id (primary key, underlined), First_Name, Last_Name.
• Relationship Supervise: a diamond between the two entity rectangles. Because it is M:N, it becomes its own table with Teacher_id and Student_id as foreign keys that together form the composite key.

Uses of data mining:

1. Finding hidden patterns and relations in large data sets.
2. Market basket analysis and customer segmentation.
3. Fraud detection (banking, insurance, credit cards).
4. Prediction and forecasting of sales and trends.
5. Customer relationship management and retention.
6. Medical diagnosis and scientific research.

A primary key uniquely identifies each record of its own table; it cannot be null or duplicated, and a table has only one. A foreign key is a field in one table that refers to the primary key of another table to link them; it may contain duplicate or null values, and a table can have several.

A genetic algorithm is a search and optimisation technique inspired by natural selection. It evolves a population of candidate solutions through selection, crossover and mutation, guided by a fitness function, until a best or near-best solution is found.

Cyber law is the body of law that governs the use of computers, the internet and electronic communication. It covers cyber crime, electronic transactions, digital signatures, privacy and intellectual property in cyberspace. In Nepal it is the Electronic Transactions Act, 2063.

Spyware is malicious software that is secretly installed on a computer and monitors the user's activities, such as keystrokes, browsing history and passwords. It sends this information to a third party without the user's knowledge.

System: a set of interrelated components that work together toward a common goal, taking input, processing it and producing output, e.g. a payroll system or an accounting system.

Implementing a new system where an old one exists (system conversion or changeover) can be done in four ways:

1. Direct (abrupt) changeover: the old system is stopped and the new one starts at once. It is fast and cheap but risky, because there is no fallback if the new system fails.
2. Parallel conversion: both systems run together for a period and their outputs are compared. It is safe but costly because the work is done twice.
3. Pilot conversion: the new system is first installed in one department or branch. After it succeeds there, it is rolled out to the others.
4. Phased conversion: the new system is introduced module by module in stages, with the old system being replaced gradually.

Before changeover, staff are trained and the old data is converted to the new format.

Scripting language: a programming language used to write small programs (scripts) that are interpreted at run time rather than compiled. Scripts automate tasks and add dynamic behaviour to web pages. Examples are JavaScript, PHP, Python and VBScript.

Data and message security means protecting data from unauthorised access, change, loss and disclosure. It can be achieved by:

1. Passwords and authentication: strong passwords, biometrics and two-factor authentication to confirm identity.
2. Encryption: converting data into unreadable cipher text, which only a holder of the key can decrypt. This protects messages in transit and stored data.
3. Digital signatures and certificates: prove the sender's identity and that the message was not altered.
4. Firewalls: filter network traffic and block unauthorised access.
5. Antivirus and anti-malware software: detect and remove malicious programs.
6. Backups: regular copies kept so that data can be restored after loss.
7. Access control and physical security: user permissions, locked server rooms and audit logs.

Layers of a neural network:

1. Input layer
2. Hidden layer(s)
3. Output layer

Expert system: an AI program that holds the knowledge of human experts in a particular field and uses it to solve problems and give advice, e.g. medical diagnosis (MYCIN).

Components:

• Knowledge base: facts and rules (usually IF-THEN) about the domain.
• Inference engine: applies the rules to the facts to reach conclusions, by forward or backward chaining.
• User interface: lets the user enter questions and see the results.
• Explanation facility: explains how and why a conclusion was reached.
• Knowledge acquisition facility: helps experts add or update knowledge.

Internet: a worldwide network of interconnected computer networks that use the TCP/IP protocol suite to exchange data. It provides services such as the web, email, file transfer and social media.

Star topology: every node (computer) is connected by its own cable to a central device, a hub or switch. All data passes through the central device.

• Advantages: easy to install and extend; a failure of one cable or node does not affect the others; faults are easy to find.
• Disadvantages: if the central hub fails the whole network goes down; it needs more cable and the hub costs extra.

Office productivity tools help an organisation do its work faster, more accurately and at lower cost.

Word processor (e.g. MS Word):

• Used to prepare letters, reports, notices, memos and contracts.
• Editing, formatting, spell check and templates give professional documents quickly.
• Mail merge sends personalised letters to many people.
• Documents can be saved, reused, shared and printed.

Spreadsheet (e.g. MS Excel):

• Stores data in rows and columns and calculates automatically with formulas and functions.
• Used for budgets, accounts, payroll, sales records and statistics.
• Charts and graphs show results visually.
• Changing one value updates all the results, which supports what-if analysis and decisions.

Presentation tool (e.g. MS PowerPoint):

• Used to prepare slides with text, images, charts, animation and sound.
• Helps staff present plans, proposals, training and reports clearly to an audience.

Together these tools reduce paperwork, save time, reduce errors, improve communication and support better decisions, so work is done effectively and efficiently.

1. Start
2. Read three numbers a, b and c from the user
3. Set sum = a + b + c
4. Print sum
5. Stop

For example, for inputs 5, 7 and 3 the sum is $5 + 7 + 3 = 15$.

Factors to consider when purchasing a computer system:

1. Purpose and the application software needed.
2. Processor speed, RAM size and storage capacity.
3. Cost and budget.
4. Brand reputation, warranty and after-sales service.
5. Compatibility and upgradability.
6. Input/output devices, ports and connectivity.
7. Operating system and software support.
8. Reliability, power use and portability.

Machine-level language is written in binary (0s and 1s), is the only language the CPU understands directly, needs no translator, is machine dependent and is very hard to write and debug. A high-level language uses English-like statements, is easy to learn, write and debug, and is machine independent (portable), but it must be translated into machine code by a compiler or interpreter.

The maintenance phase begins after the system is delivered and lasts for the rest of its working life, which may be many years. During this time errors are corrected, changes are made as business needs and technology change, and the system is improved and updated. All the earlier phases finish once, so maintenance is the longest and most costly phase.

Voice communication is the transmission of spoken words between two or more people over a communication network, either as analogue signals on telephone lines or as digital data in mobile calls and VoIP. It is real-time two-way communication.

DNS (Domain Name System) is used to convert easy-to-remember domain names such as www.google.com into the numeric IP addresses that computers use to locate each other. This lets users reach websites without remembering IP addresses.

Uses of a data warehouse:

1. Stores integrated historical data from many sources in one place.
2. Supports decision making and business intelligence.
3. Supports reporting, analysis and OLAP.
4. Identifies trends and helps forecasting.
5. Provides the base for data mining.
6. Improves data quality and consistency.

A mouse is a hand-held pointing input device. Moving it over a surface moves a pointer on the screen, and its buttons and scroll wheel are used to select, click, drag and scroll in a graphical user interface.

Soft lifting is the illegal sharing or copying of a legally purchased software for use on more than one computer, beyond what the licence allows (for example, installing one single-user copy on several office PCs or lending it to friends).

Software counterfeiting is the illegal duplication and sale of copyrighted software made to look like the genuine product, with fake packaging, manuals and licence labels, usually for profit.

• Norton Antivirus
• McAfee VirusScan
• Kaspersky Anti-Virus

(Avast, AVG and Windows Defender are also common examples.)

Logic: start with $N = 2$, display it, then add 2 and repeat until $N$ exceeds 50. This displays 2, 4, 6, ..., 50 in ascending order.

Flowchart (in text form):

      ┌─────────┐
      │  START  │
      └────┬────┘
           ▼
      ┌─────────┐
      │ N = 2   │
      └────┬────┘
           ▼
     ◇───────────◇   No
     │ N <= 50 ? │────────► ┌────────┐
     ◇───────────◇          │  STOP  │
           │ Yes            └────────┘
           ▼
     ╱─────────────╲
     │ Display N   │
     ╲─────────────╱
           ▼
      ┌─────────┐
      │N = N + 2│
      └────┬────┘
           │
           └──────► (back to the decision N <= 50 ?)

Symbols used: oval for START/STOP, rectangle for the processes $N = 2$ and $N = N + 2$, diamond for the decision $N \le 50$, parallelogram for the output "Display N". The arrow from $N = N + 2$ returns to the decision box, forming the loop.

Algorithm:

1. Start
2. Set $N = 2$
3. If $N > 50$, go to step 6
4. Display $N$
5. $N = N + 2$; go to step 3
6. Stop

Coaxial cable is a transmission medium with a central copper conductor surrounded by an insulating layer, a metallic (braided) shield and an outer plastic jacket. It carries electrical signals, is used in cable TV and older Ethernet (10Base2/10Base5), and supports moderate bandwidth over a few hundred metres.

Optical fibre is a thin strand of glass or plastic that carries data as pulses of light. It has a core, a cladding that reflects light back into the core by total internal reflection, and a protective coating. It is of two types: single-mode and multi-mode.

Comparison

Which is better: optical fibre is better technically because of its much higher speed, longer distance, low attenuation, and immunity to interference and eavesdropping. Coaxial cable is preferred only where cost and easy installation matter more.

Bus: A bus is a set of parallel wires or lines that carries data, addresses and control signals between the CPU, memory and I/O devices inside a computer.

Why different types of bus are required: each kind of information has a different direction, width and purpose, so separate buses allow them to travel at the same time without confusion.

• Data bus carries the actual data between CPU, memory and I/O. It is bidirectional, and its width (8, 16, 32, 64 bits) determines how much data moves at once.
• Address bus carries the memory or I/O address that the CPU wants to access. It is unidirectional (CPU to memory), and its width decides the maximum addressable memory ($2^n$ locations for $n$ lines).
• Control bus carries control and timing signals such as read, write, interrupt and clock, which coordinate all operations.

Using separate buses makes the system faster, organised and able to support devices of different speeds. Without them, data, addresses and commands would clash on the same lines.

Client-server architecture is a network model in which tasks are divided between service providers called servers and service requesters called clients. Clients send requests over the network and the server processes them and returns the results. Examples are web browsing, email and database access.

Characteristics of a client

• Initiates the communication by sending requests to the server.
• Waits for and receives the server's reply.
• Usually runs on a user's PC and has a user interface.
• Does not share its resources with others, and can connect to many servers.

Characteristics of a server

• Passively waits for client requests and then responds.
• Is a powerful machine with large storage, memory and processing capacity.
• Serves many clients at the same time.
• Provides centralised services such as files, printing, web and database, and controls security, backup and access.
• Runs continuously (24 hours).

Advantages: centralised management and security, easy resource sharing, easy upgrading. Disadvantage: if the server fails, all clients are affected.

Cryptography is the science and art of securing information by converting it into an unreadable form (encryption) so that only the intended person can convert it back to readable form (decryption) using a key. The original message is called plaintext and the coded message is ciphertext.

Importance of data and message encryption

1. Confidentiality: only authorised persons can read the data, even if it is intercepted during transmission or stolen.
2. Integrity: with digital signatures and hashes, any change to the message can be detected.
3. Authentication: it confirms the identity of the sender and receiver.
4. Non-repudiation: the sender cannot deny having sent a message signed with their key.
5. Safe e-commerce and banking: passwords, card numbers and online transactions (HTTPS/SSL) are protected.
6. Privacy and legal compliance: personal, medical and official data are kept private, and protection against hackers and spies is improved.

Encryption is of two main kinds: symmetric (same key for both, e.g. AES) and asymmetric (public and private keys, e.g. RSA).

• Clock speed of the processor (GHz)
• Size of RAM
• Cache memory size
• Number of processor cores and word size (bus width)
• Speed of the hard disk or storage (SSD is faster than HDD)
• Graphics card
• Type of software and number of programs running

The TCP/IP model has four layers (from top to bottom):

1. Application layer
2. Transport layer
3. Internet (Network) layer
4. Network access (Link / Network interface) layer

A language translator is a system program that converts a program written in a high-level or assembly language (source code) into machine language (object code) that the computer can understand. The three types are the assembler, the compiler and the interpreter.

A knowledge base is an organised collection of facts, rules and relationships about a particular subject area, stored in a computer so that an AI or expert system can use it for reasoning and problem solving. It is the core component of an expert system and holds the expertise gathered from human experts, usually as IF-THEN rules.

Spyware is a malicious software that is secretly installed on a computer and secretly collects information about the user's activities, such as browsing habits, passwords and banking details, and sends it to another person without the user's knowledge or consent. It also slows down the system and displays unwanted advertisements.

Encryption is the process of converting readable data (plaintext) into an unreadable coded form (ciphertext) using an algorithm and a key, so that unauthorised persons cannot understand it. The original data is recovered by decryption. It protects the security and privacy of data in storage and transmission.

The standard symbols of an E-R diagram are:

In the diagram, a key attribute has its name underlined.

Computer network: a computer network is a collection of two or more computers and devices connected by communication media (wired or wireless) to share data, hardware, software and other resources.

Types of network on the basis of area covered

1. PAN (Personal Area Network): covers a very small area of a few metres around one person, e.g. a mobile phone linked to earphones or a laptop by Bluetooth.
2. LAN (Local Area Network): covers a small area such as a room, building, school or office (up to a few km). It has high speed and low cost and is usually privately owned, e.g. a college computer lab.
3. MAN (Metropolitan Area Network): covers a city or large campus (about 5 to 50 km), connecting several LANs, e.g. a cable TV network or a bank's branches in Kathmandu valley.
4. WAN (Wide Area Network): covers a large geographical area such as a country, continent or the whole world, using telephone lines, satellites or fibre. It has lower speed and higher cost, e.g. the Internet.

Applications of AI:

• Expert systems (medical diagnosis, finance)
• Natural language processing and speech recognition (voice assistants)
• Robotics and industrial automation
• Computer vision and face or image recognition
• Game playing (chess)
• Machine translation
• Self-driving vehicles
• Fraud detection and recommendations in business

Components of an expert system

• Knowledge base: facts and IF-THEN rules collected from experts.
• Inference engine: applies the rules to the facts to draw conclusions.
• User interface: the means by which the user asks questions and receives advice.
• Explanation facility: shows how and why a conclusion was reached.
• Knowledge acquisition facility: used to add and update knowledge.

Data mining is the process of analysing large amounts of data stored in databases or data warehouses to discover hidden patterns, relationships, trends and useful knowledge that can support decision making. It uses techniques from statistics, machine learning and databases, and is also called knowledge discovery in databases (KDD).

Main tasks: classification, clustering, association rule discovery, prediction and detection of outliers.

Steps: data cleaning and selection, data transformation, applying mining algorithms, then evaluating and presenting the patterns.

Example: a supermarket analyses its sales records and finds that customers who buy bread also buy butter and milk (market-basket analysis). It places these items close together and gives combined offers to raise sales. Banks similarly use data mining to detect credit card fraud and to predict which customers may default on loans.

Algorithm:

1. Start
2. Input two numbers $A$ and $B$
3. Calculate $SUM = A + B$
4. Display $SUM$
5. Stop

Flowchart (in text form):

   ┌─────────┐
   │  START  │
   └────┬────┘
        ▼
   ╱─────────────╲
   │ Input A, B  │
   ╲─────────────╱
        ▼
   ┌─────────────┐
   │ SUM = A + B │
   └──────┬──────┘
          ▼
   ╱─────────────╲
   │ Display SUM │
   ╲─────────────╱
          ▼
   ┌─────────┐
   │  STOP   │
   └─────────┘

Ovals show the start and stop, parallelograms show input and output, and the rectangle shows the calculation. For example, if $A = 5$ and $B = 7$, then $SUM = 12$.

Bus: a bus is a group of parallel conductors (lines) that carries data, addresses and control signals between the CPU, memory and input/output devices.

Types of bus

1. Data bus: carries data between the CPU, memory and I/O devices. It is bidirectional, and its width (e.g. 32 or 64 bits) decides how many bits move together.
2. Address bus: carries the address of the memory location or I/O device that the CPU wants to access. It is unidirectional, from the CPU outwards. With $n$ address lines, $2^n$ locations can be addressed.
3. Control bus: carries control and timing signals such as memory read/write, I/O read/write, interrupt request and clock, to coordinate and synchronise the operations of all components.

Buses are also classified as internal (system) bus inside the CPU and motherboard, and external (expansion) bus such as USB, PCI and SATA used to connect peripherals.

System: a system is a set of interrelated components that work together to achieve a common goal. It has inputs, processes, outputs and feedback, e.g. a library system or an examination system.

Development phase of the System Development Life Cycle (SDLC)

In this phase the design of the new system is turned into a working system. It includes:

1. Software development: programmers write, compile and debug the programs in a suitable programming language following the design specification, or the software is purchased or customised.
2. Hardware acquisition: the required computers, network devices and other equipment are selected and bought or installed.
3. Database creation: the files and database tables are set up.
4. Testing: unit testing of modules, integration testing of modules together, system testing of the entire system and user acceptance testing, to find and correct errors.
5. Documentation: the user manual, technical manual and operating instructions are prepared.
6. Training: the users and operators are prepared to use the system.

The completed and tested system then moves on to the implementation phase.

Cryptography: cryptography is the technique of securing information by converting plaintext into unreadable ciphertext with an algorithm and key (encryption), so that only the person who holds the correct key can decrypt and read it. Its two main types are symmetric key (one shared key, e.g. AES) and public key (a public/private key pair, e.g. RSA).

Why it is necessary in email communication

1. Confidentiality: an email passes through many servers and routers, where it can be intercepted. Encryption makes it unreadable to eavesdroppers and hackers.
2. Authentication: a digital signature proves the sender's identity and prevents forged or spoofed emails.
3. Integrity: it shows that the message was not changed on the way.
4. Non-repudiation: the sender cannot deny having sent the mail.
5. Privacy of sensitive content: passwords, bank details, business and personal information are protected, as in PGP and S/MIME.

Random Access Memory (RAM) is the main (primary) memory of a computer that temporarily stores the programs and data currently in use by the CPU. Any location can be read or written directly in equal time. It is volatile, so its contents are lost when the power is switched off. DRAM and SRAM are its main types.

System analysis is done to study the existing system in detail and understand its working, problems and limitations. It finds out the requirements of the users and what the new system should do, and decides whether a new system is feasible, so that a proper and cost-effective system can be designed.

Remote login (e.g. Telnet, SSH) lets a user log in to and use a distant computer over a network as if sitting at it. Its advantages are:

• Access to files, programs and powerful machines from anywhere.
• Saves time and travel cost.
• Allows remote administration, support and troubleshooting of systems.
• Helps share expensive resources.

A firewall is a hardware or software security system that monitors and controls incoming and outgoing network traffic according to security rules. It stands between a trusted internal network and an untrusted network such as the Internet and blocks unauthorised access and attacks while allowing legitimate traffic.

Software testing is the process of running a program or system with test data to find errors and to check that it works correctly and meets the user's requirements. It ensures the quality and reliability of the software before delivery. Its types include unit, integration, system and acceptance testing.

The Domain Name System (DNS) translates human-readable domain names (e.g. www.google.com) into numeric IP addresses that computers use to locate each other. This means users need not remember long IP addresses, and it makes browsing and email easy.

Software: software is a set of programs, instructions and data that tells the computer hardware what to do and how to do it. It is of two main kinds: system software (operating system, translators, utilities) and application software (word processors, spreadsheets, etc.).

Five uses of an application software (MS Word, a word processor)

1. Typing and creating letters, reports, applications and books.
2. Editing and formatting text, with fonts, sizes, colours, alignment and spacing.
3. Inserting tables, pictures, charts and shapes in documents.
4. Checking spelling and grammar, and using find and replace.
5. Saving, printing and sharing documents, and making mail merges for many letters.

Data warehouse: a data warehouse is a large, central, subject-oriented, integrated, time-variant and non-volatile repository of data collected from many different sources (operational databases, files, etc.) of an organisation, stored for analysis and reporting rather than for daily transactions.

Why a data warehouse is created

1. To integrate data from different sources into one consistent place.
2. To support decision making, with reports, queries and OLAP, by giving managers a complete view of the business.
3. To keep historical data for trend analysis and forecasting.
4. To separate analysis from the operational systems, so that daily transaction processing is not slowed down.
5. To serve as the base for data mining and business intelligence.

Algorithm:

1. Start
2. Set $SUM = 0$
3. $SUM = SUM + 222$
4. $SUM = SUM + 333$
5. $SUM = SUM + 444$
6. $SUM = SUM + 555$
7. Display $SUM$
8. Stop

Check: $222 + 333 + 444 + 555 = 1554$, so the algorithm displays 1554.

Network: a network is a group of two or more computers and devices connected together by cables or wireless media to share data, hardware and software resources and to communicate.

Star topology: in a star topology, every node is connected to a central device (hub or switch).

Advantages of star topology

1. Easy to install, expand and reconfigure: a new node can be added without disturbing the network.
2. Failure of one node or cable does not affect the others.
3. Faults are easy to detect and isolate, since each node has its own link.
4. Centralised management and control.
5. Good performance, as each device has a dedicated connection to the centre (with a switch).

Primary storage (main memory: RAM, ROM, cache)

• Holds the programs and data currently being processed so that the CPU can access them directly and quickly.
• Stores intermediate results and instructions during execution.
• ROM stores the permanent start-up (boot) instructions.
• Cache gives very fast access to frequently used data.

Secondary storage (hard disk, SSD, CD/DVD, pen drive)

• Stores programs and data permanently (non-volatile), even when the power is off.
• Gives large storage capacity at lower cost per byte.
• Used for backup and archiving of data.
• Used to transfer data between computers (portable devices).
• Holds the operating system and application software until needed in RAM.

System: A system is a set of interrelated components that work together toward a common goal by accepting inputs, processing them and producing outputs, e.g. a library management system or a payroll system.

Conversion strategies (changing from the old system to the new one):

• Direct (abrupt) conversion: the old system is stopped and the new one starts at once. It is cheap and quick but very risky if the new system fails.
• Parallel conversion: old and new systems run together for some time and their outputs are compared. It is the safest, but costly because of double work.
• Pilot conversion: the new system is first installed in one branch or department and then extended to the rest.
• Phased conversion: the new system is introduced module by module in stages.

Best strategy: In my view parallel conversion is best for important systems such as banking or accounting. The old system acts as a backup, errors in the new system can be detected by comparing results, users get time to learn the system, and there is no loss of data or service if the new system fails. Its extra cost is justified by the reduced risk. For a very large organisation, pilot conversion is a good alternative.

Artificial Intelligence (AI) is the branch of computer science that builds machines and software able to perform tasks that normally need human intelligence, such as learning, reasoning, problem solving, understanding language and recognising images.

Importance of AI:

• Automation of repetitive work: AI performs routine tasks faster and without fatigue, saving time and cost.
• Accuracy and fewer errors: AI systems make consistent decisions and reduce human error, e.g. in medical diagnosis and banking fraud detection.
• Decision support: AI analyses large amounts of data to give useful predictions and recommendations to managers.
• Work in dangerous areas: Robots can work in mines, space, deep sea and disaster zones where humans are at risk.
• 24-hour availability: Chatbots and virtual assistants serve customers at any time.
• Better services: AI is used in education, agriculture, transport (self-driving), speech recognition, translation and search engines.

RAM (Random Access Memory) is the main, volatile memory of a computer that temporarily holds the programs and data currently in use by the CPU. Its contents are lost when the power is switched off, and it can be read from and written to quickly.

Software is a set of programs, instructions and data that tells the computer hardware what to do. Examples: Windows (system software), MS Word (application software).

The address bus carries the memory address (location) of the data or instruction that the CPU wants to read or write. It is unidirectional, from the CPU to memory and I/O devices, and its width decides how much memory can be addressed ($2^n$ locations for an $n$-bit bus).

Characteristics of OOP:

• Class and object
• Encapsulation
• Data abstraction
• Inheritance
• Polymorphism
• Data hiding and message passing

A feasibility study is a preliminary investigation done in the early phase of system development to decide whether the proposed system is practical and worthwhile. It examines technical, economic, operational and schedule feasibility before the project is approved.

Sequential file processing is a method in which records are stored and processed one after another in the order in which they were written (often sorted by a key). To reach a particular record, all the records before it must be read, e.g. payroll processing from magnetic tape.

An FTP client is a software program that connects to an FTP (File Transfer Protocol) server so that a user can upload files to, download files from, and manage files on a remote computer over a network. Examples: FileZilla and WinSCP.

A primary key is a field (or combination of fields) in a table whose value uniquely identifies each record. It can neither be duplicated nor be null, e.g. Roll_No in a Student table.

A neural network (artificial neural network) is a computing model inspired by the human brain. It consists of interconnected nodes (artificial neurons) arranged in layers that learn patterns from data by adjusting the weights of their connections. It is used in image recognition, speech recognition and prediction.

Cyber law is the set of legal rules that governs the use of computers, the Internet and digital information. It deals with crimes such as hacking, piracy, identity theft and online fraud, and with electronic transactions, digital signatures and privacy. In Nepal it is the Electronic Transactions Act, 2063 (2008).

Characteristics of a monitor:

• Screen size: the diagonal length of the display, in inches.
• Resolution: number of pixels horizontally by vertically, e.g. 1920 x 1080; higher resolution gives a sharper image.
• Refresh rate: how many times per second the screen is redrawn (Hz); a higher rate reduces flicker.
• Dot (pixel) pitch: distance between pixels; a smaller pitch gives a clearer image.
• Colour depth: the number of colours that can be displayed.
• Aspect ratio and response time, e.g. 16:9.

Difference between LED and LCD monitors:

An image file format is a standard way of storing a digital image in a file, specifying how pixel data, colour and compression are organised, e.g. JPEG, PNG, GIF, BMP and TIFF.

Characteristics of JPEG:

• Uses lossy compression, giving small files by discarding some detail.
• Supports about 16.7 million colours (24-bit), so it is ideal for photographs.
• Compression level can be adjusted, trading quality for size.
• Does not support transparency or animation.
• Quality degrades if the image is repeatedly edited and saved.

Characteristics of PNG:

• Uses lossless compression, so no quality is lost.
• Supports transparency (alpha channel) and up to 24-bit colour.
• Best for logos, graphics, screenshots and text images.
• File size is larger than JPEG for photographs.

The $i$-th term is $\frac{i!}{i}=(i-1)!$, so we compute the factorial incrementally.

Algorithm:

1. Start.
2. Read $N$.
3. Set $sum = 0$, $fact = 1$ (this holds $(i-1)!$).
4. For $i = 1$ to $N$:
   • $sum = sum + fact$
   • $fact = fact \times i$
5. Display $sum$.
6. Stop.

Check ($N=4$): terms are $1, 1, 2, 6$, so $sum = 10$. Direct: $\frac{1!}{1}+\frac{2!}{2}+\frac{3!}{3}+\frac{4!}{4}=1+1+2+6=10$.

Guided media (wired or bounded media) are transmission media in which signals travel along a physical path such as a cable. Examples: twisted pair, coaxial cable and optical fibre.

Optical fibre: It is a thin strand of glass or plastic that carries data as pulses of light. It has three parts: the core (carries light), the cladding (a layer of lower refractive index that keeps light inside by total internal reflection) and the protective jacket.

• Advantages: very high bandwidth and speed, low signal loss over long distances, immune to electromagnetic interference, secure, and light weight.
• Disadvantages: expensive, difficult to install and repair, and fragile.

Types are single-mode fibre (long distance) and multi-mode fibre (short distance).

• Search engine: a software system that searches the Web for information using keywords and displays a ranked list of results, e.g. Google and Bing.
• HTTP (HyperText Transfer Protocol): the application-layer protocol used to transfer web pages and other resources between a web server and a browser.
• WWW (World Wide Web): a global collection of interlinked hypertext documents and multimedia resources stored on web servers and accessed through the Internet using URLs.
• Web browser: application software used to access, retrieve and display web pages, e.g. Chrome, Firefox and Edge.

Artificial Intelligence (AI) is the ability of a computer or machine to imitate human intelligence, such as learning from experience, reasoning, understanding language, recognising patterns and making decisions.

Importance of AI:

• Automates repetitive and time-consuming tasks, saving time and cost.
• Reduces human errors and gives consistent, accurate results.
• Helps in decision making by analysing large amounts of data quickly.
• Works in dangerous environments (space, mines, disaster areas) through robots.
• Provides round-the-clock service through chatbots and virtual assistants.
• Improves fields such as medicine (diagnosis), education, agriculture, banking (fraud detection) and transport (self-driving vehicles).
• Enables speech recognition, language translation and smart search.

Data processing is the series of operations carried out on raw data to convert it into meaningful information. The main steps are data collection, input and verification, sorting, calculation/processing, storage and output (reporting).

Why data processing is needed:

• Raw data has no meaning by itself; processing turns it into useful information.
• It provides accurate and timely information for decision making.
• It saves time and effort compared with manual handling of large volumes of data.
• It reduces errors and improves accuracy.
• It allows data to be organised, stored and retrieved easily for later use.
• It supports reports, planning, control and analysis in organisations, e.g. payroll, billing and results.

Input devices are hardware used to enter data and instructions into a computer, e.g. keyboard, mouse, scanner, microphone and webcam.

Output devices present the results of processing to the user, e.g. monitor, printer, speaker and projector.

Storage devices hold data and programs permanently or semi-permanently, e.g. hard disk, SSD, CD/DVD, pen drive and memory card. Primary storage (RAM/ROM) is internal and secondary storage is external or permanent.

Factors affecting computer performance:

• Processor (CPU) speed and cores: a higher clock speed (GHz) and more cores execute more instructions per second.
• RAM size and speed: more RAM allows more programs to run without slow swapping to disk.
• Cache memory: fast cache reduces the time the CPU waits for data.
• Storage type and speed: an SSD is much faster than an HDD.
• Bus width and speed: a wider and faster data bus transfers more data per cycle.
• Graphics card: important for video, games and design.
• Operating system and software: efficient, up-to-date software runs better; too many background programs slow the system.
• Viruses and malware, and disk fragmentation: reduce speed.
• Heat and cooling: overheating makes the CPU slow down.

Algorithm:

1. Start.
2. Set $n = 0$.
3. If $n > 59$, go to step 7.
4. If $n \bmod 18 = 0$, display $n$.
5. Set $n = n + 1$.
6. Go to step 3.
7. Stop.

Output: 0, 18, 36, 54.

Flow chart (in text form):

      [ Start ]
          |
      [ n = 0 ]
          |
   +----->|
   |  < n <= 59 ? > --No--> [ Stop ]
   |      | Yes
   |  < n mod 18 = 0 ? > --No--+
   |      | Yes                |
   |  [ Display n ]             |
   |      |                     |
   |      +<--------------------+
   |      |
   |  [ n = n + 1 ]
   |      |
   +------+

An efficient alternative is to start with $n = 0$ and add 18 each time until $n > 59$, which prints the same numbers.

System analysis phase of SDLC: After the preliminary investigation and feasibility study, system analysis is the phase in which the analyst studies the existing system in detail to understand how it works, its problems and the users' needs, and then defines the requirements of the new system. Activities include fact finding (interviews, questionnaires, observation, document review), analysing the data and processes (using DFDs, ER diagrams and data dictionary), identifying problems, and preparing the System Requirement Specification (SRS).

Technical document vs. user document:

Image quality is the degree of clarity, sharpness, colour accuracy and detail of a digital image. It depends mainly on resolution (number of pixels), colour depth (bits per pixel), the compression used and the file format.

Three types of image file format:

1. JPEG (.jpg): Uses lossy compression to give small files. Supports 24-bit colour, so it is best for photographs and web images. It does not support transparency, and repeated saving lowers quality.
2. PNG (.png): Uses lossless compression, so quality is retained. Supports transparency and 24-bit colour, so it is good for logos, screenshots and web graphics. Files are larger than JPEG for photos.
3. GIF (.gif): Limited to 256 colours (8-bit) with lossless compression. Supports simple animation and transparency, so it is suitable for icons and small animations, but not for photographs.

Other formats are BMP (uncompressed, large) and TIFF (high quality, used in printing and scanning).

Computer network: A computer network is a collection of two or more computers and other devices connected by communication media so that they can share data, resources and information.

Advantages:

• Resource sharing: printers, scanners, storage and software can be shared, reducing cost.
• Data and file sharing: users can exchange files quickly.
• Communication: email, chat and video conferencing connect people.
• Centralised data and backup: data is stored on a server, which makes management, security and backup easier.
• Cost saving: software licences and hardware are used more efficiently.
• Reliability: data can be kept on more than one computer, so work continues if one fails.
• Remote access and online services.

Disadvantages:

• High initial cost of equipment, cabling and setup.
• Security risks such as hacking, viruses and unauthorised access.
• If the server or main link fails, the whole network may stop.
• Needs skilled administrators for maintenance.
• Dependence on the network and possible privacy problems.

Primary key: a field or set of fields that uniquely identifies each record in a table; it cannot be duplicate or null, e.g. E_ID in Employee.

Foreign key: a field in one table that refers to the primary key of another table and is used to link the two tables, e.g. C_ID in works_in refers to C_ID of company.

E-R diagram:

Entities: Employee and Company; relationship: works_in.

 [ Employee ] -------< works_in >------- [ Company ]
      N                                       M

 Employee attributes:  E_ID (PK), E_Name, Street, City, Salary
 Company attributes:   C_ID (PK), C_Name, Location
 works_in:             E_ID (FK), C_ID (FK)

In the diagram, Employee and Company are drawn as rectangles, works_in as a diamond, and the attributes as ovals connected to their entity (E_ID and C_ID underlined as primary keys). The cardinality is many-to-many: an employee may work in more than one company and a company has many employees. The relationship is implemented by the table works_in(E_ID, C_ID) whose two columns are foreign keys referencing Employee and company.

Artificial Intelligence (AI) is the branch of computer science concerned with making computers and machines perform tasks that normally require human intelligence, such as learning, reasoning, problem solving, perception and understanding language.

Two uses of AI:

1. Healthcare: AI analyses medical images (X-ray, MRI, CT) and patient records to detect diseases such as cancer early, suggests treatments, and helps in drug discovery and robotic surgery. It improves accuracy and speed of diagnosis.
2. Virtual assistants and chatbots (natural language processing and speech recognition): Systems such as Siri, Google Assistant and customer-service chatbots understand speech or text, answer questions, translate languages and perform tasks, giving service 24 hours a day.

Other uses include self-driving vehicles, fraud detection in banking, robotics and recommendation systems.

Cryptography is the science and practice of securing information by converting it into a form that unauthorised persons cannot understand. It provides confidentiality, integrity, authentication and non-repudiation.

Encryption is the process of converting readable data (plaintext) into an unreadable form (ciphertext) using an algorithm and a key.

Decryption is the reverse process of converting the ciphertext back into the original plaintext using the correct key.

Plaintext --(Encryption + key)--> Ciphertext --(Decryption + key)--> Plaintext

Types:

• Symmetric key: the same key is used for encryption and decryption (e.g. AES, DES).
• Asymmetric key: a public key encrypts and a private key decrypts (e.g. RSA).

Example (Caesar cipher with shift 3): Each letter is replaced by the letter three places later.

• Plaintext: HELLO
• Encryption: H to K, E to H, L to O, L to O, O to R, giving ciphertext KHOOR.
• Decryption: shift each letter back by 3, so KHOOR becomes HELLO.

Here the shift value 3 is the key.

Two characteristics of a computer: (1) speed, as it performs millions of operations per second; (2) accuracy, as it gives precise results. Others: diligence, storage capacity and versatility.

PROM (Programmable ROM) can be programmed only once by the user after manufacture and cannot be erased. EPROM (Erasable PROM) can be erased by exposing it to ultraviolet light and then reprogrammed many times.

Antivirus software (e.g. Kaspersky, Avast) and disk defragmenter (or file compression tools such as WinRAR, and backup tools).

Plasma displays consume a lot of power, produce heat, are heavy and thick, and are fragile, so they drain the battery quickly and are unsuitable for small portable hand held devices. LCD/LED/OLED screens are used instead.

Client-side scripting (e.g. JavaScript) runs in the user's browser, so it validates form input instantly without contacting the server, reduces server load and network traffic, gives faster response, and makes web pages interactive and dynamic (menus, animations, dynamic content).

A system is a set of interrelated components that work together to achieve a common goal by taking inputs, processing them and producing outputs.

Radio waves and microwaves (also infrared and satellite communication).

Language translators (compiler, interpreter and assembler) are used to convert programs written in assembly or high-level languages into machine language (binary), which is the only language the computer's processor can understand and execute.

Antipiracy refers to the laws, techniques and measures (such as licensing, product keys, activation, watermarks and copyright enforcement) used to prevent the illegal copying, distribution and use of software, music, films and other digital content.

Output devices are used to present the results of processing to the user in a human-readable form (text, graphics, sound or video), because the computer's internal data is in binary and cannot be understood directly.

Two output devices:

• Monitor: a soft-copy output device that displays text, images and video on a screen. Types include CRT, LCD and LED. Its quality depends on resolution, size and refresh rate.
• Printer: a hard-copy output device that prints text and graphics on paper. Types include dot-matrix, inkjet and laser printers; laser printers give fast, high-quality output.

Multimedia is the combination of several forms of content, such as text, graphics, images, audio, video and animation, delivered through a computer or digital device in an interactive way. Examples: educational software, video games and websites.

Differences between TIF and JPEG:

The series is the squares of 10 down to 1: $10^2, 9^2, \dots, 1^2$.

Algorithm:

1. Start.
2. Set $i = 10$.
3. If $i < 1$, go to step 7.
4. Display $i \times i$.
5. Set $i = i - 1$.
6. Go to step 3.
7. Stop.

Output: 100, 81, 64, 49, 36, 25, 16, 9, 4, 1.

Topology is the physical or logical layout of how computers, cables and other devices are arranged and connected in a network.

Types of topology

1. Bus topology: All devices connect to one common backbone cable. It is cheap and easy to install, but a break in the backbone stops the whole network and performance falls as traffic grows.
2. Star topology: Every device connects to a central hub or switch. A failure of one cable affects only one device and faults are easy to find, but if the central device fails, the whole network fails.
3. Ring topology: Each device connects to exactly two neighbours, forming a closed loop, and data travels in one direction (often using a token). It gives orderly access, but one failure can break the ring.
4. Mesh topology: Every device is connected to every other device. It is very reliable, but expensive and hard to install because of the many links.
5. Tree (hybrid) topology: A combination of star and bus topologies arranged in a hierarchy. It is scalable, but depends on the root backbone.

Data and message security means protecting data stored in computers and messages sent over networks from unauthorised access, modification, theft or destruction. It aims at confidentiality, integrity and availability.

Encryption and decryption

• Encryption converts the original readable data (plaintext) into an unreadable form (ciphertext) using an algorithm and a key.
• Decryption is the reverse: ciphertext is converted back to plaintext using the matching key.

Process: Sender: plaintext -> encryption algorithm + key -> ciphertext -> sent through the network -> receiver: ciphertext -> decryption algorithm + key -> plaintext.

Example (Caesar cipher, key = 3): Each letter is shifted 3 places forward.

• Plaintext: NEPAL
• Encryption: N->Q, E->H, P->S, A->D, L->O, giving ciphertext QHSDO.
• Decryption: shift each letter 3 places back, giving NEPAL again.

Modern systems use symmetric keys (same key, e.g. AES) or asymmetric keys (public and private key pair, e.g. RSA).

Differences between sequential and direct access file processing

Steps used in data processing

1. Data collection: Gathering raw data from sources (forms, sensors, surveys).
2. Data preparation/input: Checking, coding and entering the data into the computer.
3. Processing: Sorting, calculating, classifying, summarising and comparing the data.
4. Output: Presenting results as reports, charts or displays (information).
5. Storage: Saving data and results for future use.
6. Communication/distribution: Sending the information to the users who need it.