(a) ((ABCD){16} = (?){8})

Method: Hexadecimal → Binary → Octal

Step 1: Convert each hex digit to its 4-bit binary equivalent.

So, $(ABCD)_{16} = (1010\ 1011\ 1100\ 1101)_2 = (1010101111001101)_2$

Step 2: Group the binary digits into sets of 3 bits from right to left (for octal).

$1010101111001101 = 1\ 010\ 101\ 111\ 001\ 101$

Pad the leftmost group with zeros to make it 3 bits: $001\ 010\ 101\ 111\ 001\ 101$

Step 3: Convert each 3-bit group to its octal digit.

$\boxed{(ABCD)_{16} = (125715)_8}$

Verification: ((ABCD)_{16} = 10\cdot16^3 + 11\cdot16^2 + 12\cdot16 + 13 = 40960 + 2816 + 192 + 13 = 43981) ((125715)_8 = 1\cdot8^5 + 2\cdot8^4 + 5\cdot8^3 + 7\cdot8^2 + 1\cdot8 + 5 = 32768 + 8192 + 2560 + 448 + 8 + 5 = 43981) ✓

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(b) ((1011){10} = (?){2})

Method: Repeated division by 2

Reading the remainders from bottom to top:

$\boxed{(1011)_{10} = (1111110011)_2}$

Verification: (1\cdot2^9 + 1\cdot2^8 + 1\cdot2^7 + 1\cdot2^6 + 1\cdot2^5 + 1\cdot2^4 + 0\cdot2^3 + 0\cdot2^2 + 1\cdot2^1 + 1\cdot2^0) (= 512 + 256 + 128 + 64 + 32 + 16 + 0 + 0 + 2 + 1 = 1011) ✓

1. Basics of Computer Organization (4 marks)

Computer organization refers to the way the physical units of a computer are arranged and interconnected, and how they interact to execute a program. It deals with the hardware structure (what units exist and how they are linked) rather than the abstract instruction-set design (computer architecture).

Basic functional units

Stored-program (von Neumann) concept: instructions and data are kept in the same memory in binary form; the CPU fetches them one by one and executes them. This is the basis of all modern general-purpose computers.

Instruction cycle: the CPU repeatedly performs Fetch → Decode → Execute → Store, controlled by the clock. The program counter holds the address of the next instruction; the instruction register holds the instruction being executed; the MAR/MDR handle memory transfers.

Key organizational parameters: word length (bits processed at a time), clock speed, memory capacity and access time, number of address lines (addressable memory), instruction formats and addressing modes, and the degree of pipelining/parallelism.

2. Types of Software (6 marks)

Software is the set of programs, procedures and associated data that instruct the hardware what to do. It is broadly classified as follows.

A. System Software

Software that manages and controls the hardware and provides a platform for running application programs. It is machine-dependent and usually supplied with the computer.

1. Operating system — resource manager and interface between user and hardware, e.g. Windows, Linux, UNIX, macOS, Android. Functions: process, memory, file, device and I/O management, security, user interface.
2. Language translators
   • Assembler — converts assembly language into machine code.
   • Compiler — translates a whole high-level program into machine code at once (faster execution, e.g. C, C++).
   • Interpreter — translates and executes line by line (easier debugging, slower, e.g. Python, BASIC).
3. Linker and loader — the linker joins object modules and library routines into one executable; the loader places it into memory and starts execution.
4. Device drivers — small programs that let the OS communicate with a specific device (printer, graphics card).
5. Utility software — housekeeping tools: antivirus, disk defragmenter, backup, compression (WinZip), disk cleaner, debugger.
6. Firmware / middleware — firmware is program permanently stored in ROM (BIOS); middleware connects different applications or systems (e.g. database middleware).

B. Application Software

Software written to perform a specific task useful to the user. It runs on top of system software.

1. General-purpose (packaged) software — ready-made, used by many users for many purposes: word processors (MS Word), spreadsheets (Excel), presentation tools (PowerPoint), DBMS (Access, Oracle), graphics and multimedia packages, web browsers.
2. Special-purpose (tailored/custom) software — developed for one particular organization or task: payroll system of a bank, railway reservation system, hospital management system, inventory control, accounting package of a company.
3. Utility application programs — small task-specific programs such as a calculator, notepad, media player.
4. Web-based / mobile applications — e-commerce sites, e-mail clients, social media apps, mobile banking apps.

Summary

Conclusion: Computer organization supplies the hardware framework — CPU, memory, I/O and buses working under the stored-program concept — while software, divided into system and application software, drives that hardware to produce useful results. Hardware and software together form a complete computer system.

Operating System

An operating system (OS) is system software that acts as an interface between the user and the computer hardware. It manages all hardware and software resources of the computer, provides an environment in which programs can execute, and offers services such as process management, memory management, file management, device management, and security. Examples: Windows, Linux, macOS, Android.

File Management

File management is the part of the OS that creates, organizes, stores, retrieves, and protects files on storage devices. Its main functions are:

• File creation and deletion: Provides commands/system calls to create new files and remove unwanted ones.
• Directory organization: Maintains a hierarchical structure of directories (folders) so files can be grouped and located easily.
• File naming and attributes: Each file has a name and attributes such as type, size, owner, and permissions (read, write, execute).
• Access methods: Supports sequential access (reading records one after another) and direct/random access (jumping to any record).
• Allocation of disk space: Allocates blocks to files using methods such as contiguous allocation, linked allocation, or indexed allocation.
• File operations: Provides operations like open, close, read, write, append, and seek.
• Protection and security: Controls who may read, write, or delete a file, preventing unauthorized access.
• Free space management: Tracks which disk blocks are free using bit vectors or linked lists.

Device Management

Device management is the OS function that controls and coordinates all input/output devices (keyboard, mouse, disk, printer, monitor, etc.). Its main functions are:

• Device drivers: Provides driver software that translates general I/O requests into device-specific commands.
• Device independence: Programs can access devices through a uniform interface without knowing hardware details.
• Buffering: Uses memory buffers to smooth the speed mismatch between fast CPU and slow I/O devices.
• Spooling: Queues jobs (e.g., printing) on disk so that a slow device can be shared among many processes.
• Scheduling: Decides the order in which competing processes get access to a device (e.g., FCFS, SSTF, SCAN for disks).
• Interrupt handling: Responds to device interrupts and transfers control to the appropriate handler.
• Error handling: Detects and reports device errors and takes corrective action.
• Allocation and deallocation: Assigns a device to a process exclusively or in shared mode and releases it when done.

Wireless Networking

Wireless networking is a method of connecting computers and devices without physical cables, using radio waves, microwaves, or infrared signals as the transmission medium. Devices communicate through a wireless access point (WAP) or directly with each other.

Components: wireless network interface cards (WNIC), access points, routers, and antennas.

Types:

• WPAN (Wireless Personal Area Network) — short range, e.g., Bluetooth, infrared.
• WLAN (Wireless Local Area Network) — e.g., Wi-Fi within a building or campus.
• WMAN (Wireless Metropolitan Area Network) — e.g., WiMAX covering a city.
• WWAN (Wireless Wide Area Network) — e.g., mobile networks (3G, 4G, 5G) covering large areas.

Working: A device's wireless adapter sends data as radio signals to an access point; the access point forwards the data to the wired network or to another wireless device. Data is transmitted in frames, and security is provided by protocols such as WEP, WPA, and WPA2.

Advantages: mobility, easy and cheap installation, no cabling, easy expansion, and access from remote locations.

Disadvantages: limited range, lower speed than wired networks, interference from other signals, and security risks such as unauthorized access.

Applications: Wi-Fi hotspots, mobile internet, Bluetooth headsets, satellite communication, and IoT devices.

WWW (World Wide Web) — [1]

The World Wide Web (WWW) is a system of interlinked hypertext documents and multimedia content that are accessed over the Internet using browsers. It was invented by Tim Berners-Lee in 1989 at CERN. Web pages are written in HTML, identified by URLs, and transferred using the HTTP/HTTPS protocol. The WWW is only one service of the Internet; other services include e-mail, FTP, and Telnet.

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Telnet — [1.5]

Telnet (Terminal Network) is a TCP/IP application-layer protocol that allows a user to log in to a remote computer over a network and use it as if sitting at its terminal. It works on a client–server model using port 23 and provides a command-line (text-based) interface. It is mainly used for remote administration, configuration of routers/switches, and accessing remote databases. Its major drawback is that data (including passwords) is sent in plain text, so it is insecure; it has largely been replaced by SSH.

E-mail — [1.5]

E-mail (Electronic Mail) is a service for sending and receiving text messages and file attachments electronically over a network. It works on a store-and-forward model using protocols such as SMTP (for sending), POP3 and IMAP (for receiving). Every user has a unique address of the form username@domain (e.g., ram@gmail.com). Advantages include speed, low cost, and the ability to send the same message to many recipients at once; its main problems are spam, viruses, and lack of guaranteed delivery.

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Three Types of Number Systems — [6]

A number system is defined by its base (radix) and the set of digits it uses. Three important types are described below.

(a) Decimal Number System (Base 10)

• Uses ten digits: 0–9.
• Each position has a weight that is a power of 10.
• It is the system used by humans in everyday life.

Example: ((237)_{10} = 2\times10^2 + 3\times10^1 + 7\times10^0 = 200 + 30 + 7).

(b) Binary Number System (Base 2)

• Uses only two digits: 0 and 1.
• Each position has a weight that is a power of 2.
• It is the natural language of digital computers, since a bit has two states (ON/OFF).

Example: ((1011)2 = 1\times2^3 + 0\times2^2 + 1\times2^1 + 1\times2^0 = 8 + 0 + 2 + 1 = (11){10}).

(c) Octal Number System (Base 8)

• Uses eight digits: 0–7.
• Each position has a weight that is a power of 8.
• It is used as a compact shorthand for binary, because 3 binary bits = 1 octal digit.

Example: ((347)8 = 3\times8^2 + 4\times8^1 + 7\times8^0 = 192 + 32 + 7 = (231){10}).

(d) Hexadecimal Number System (Base 16)

• Uses sixteen symbols: 0–9 and A–F, where A = 10, B = 11, … F = 15.
• Each position has a weight that is a power of 16.
• It is widely used in programming and memory addressing, since 4 binary bits = 1 hex digit.

Example: ((2AF){16} = 2\times16^2 + 10\times16^1 + 15\times16^0 = 512 + 160 + 15 = (687){10}).

Comparison

Thus the decimal system suits humans, while binary, octal and hexadecimal are convenient for representing and handling data inside computers.

Decimal to binary conversion

Method: divide the number repeatedly by 2, note the remainder at each step, and read the remainders from bottom to top.

(a) 10

Reading remainders upward: 10 = (1010)₂

(b) 12

Reading remainders upward: 12 = (1100)₂

(c) 9

Reading remainders upward: 9 = (1001)₂

(d) 8

Reading remainders upward: 8 = (1000)₂

(e) 4

Reading remainders upward: 4 = (100)₂

(f) 23

Reading remainders upward: 23 = (10111)₂

Summary

$10 = (1010)_2,\quad 12 = (1100)_2,\quad 9 = (1001)_2$ $8 = (1000)_2,\quad 4 = (100)_2,\quad 23 = (10111)_2$

Verification (by positional weights):

• $(1010)_2 = 8 + 0 + 2 + 0 = 10$ ✓
• $(1100)_2 = 8 + 4 + 0 + 0 = 12$ ✓
• $(1001)_2 = 8 + 0 + 0 + 1 = 9$ ✓
• $(1000)_2 = 8$ ✓
• $(100)_2 = 4$ ✓
• $(10111)_2 = 16 + 0 + 4 + 2 + 1 = 23$ ✓

Nano Science

Nano science is the branch of science that studies matter at the nanoscale, i.e. at dimensions roughly between 1 and 100 nanometres (1 nm = 10⁻⁹ m). At this scale, the physical, chemical, and biological properties of materials differ markedly from those at the bulk (macroscopic) scale, mainly because of two effects:

• Surface/interface effect — the fraction of atoms lying on the surface becomes very large, so surface energy and reactivity increase enormously.
• Quantum confinement effect — the motion of electrons becomes restricted in one or more directions, so electronic and optical properties become size-dependent (e.g. colour of a semiconductor changes with particle size).

Nano science is therefore the study of the synthesis, characterisation, and behaviour of nanostructures such as nanoparticles, nanotubes, nanowires, and thin films. When this knowledge is used to design useful devices and materials, it is called nano technology. It is an interdisciplinary field, drawing on physics, chemistry, biology, materials science, and engineering. Its importance lies in the fact that properties can be tuned simply by changing particle size, which is not possible in bulk materials.

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Applications of Database

A database is an organised collection of related data managed by a DBMS, which provides controlled storage, retrieval, security, and concurrent access. Its major applications are:

1. Banking and finance — storage of customer accounts, transactions, loans, and ATM/online-banking records; ensures accuracy, atomicity, and security of money transfers.
2. Airlines and railways — reservation systems, flight/train schedules, seat availability, and passenger records, queried online from many locations at once.
3. Education — student admission, marks, attendance, fee, and library records; universities also use databases for examination and result processing.
4. Hospitals — patient history, diagnosis, prescriptions, laboratory reports, and billing, allowing quick retrieval during emergencies.
5. E-commerce and retail — product catalogues, stock/inventory control, customer profiles, shopping carts, and order tracking.
6. Telecommunications — call detail records, billing, subscriber data, and network usage logs.
7. Government and administration — census, land records, taxation, voter lists, passport, and citizen identity databases.
8. Social media and web services — user accounts, posts, messages, and recommendation data; large-scale use of distributed and NoSQL databases.
9. Manufacturing and production — inventory, supply chain, production planning, and quality-control data.
10. Scientific research and data warehousing — storage and analysis of large experimental datasets, and support for decision-making through data mining.

In short, any organisation that must store large amounts of related data, retrieve it quickly, keep it consistent and secure, and share it among many users relies on database technology.

Components of Multimedia

Multimedia is the integration of different media types into a single digital presentation, controlled by a computer. Its main components are:

1. Text The most basic component. It conveys information through words, sentences and paragraphs. Text can be plain (ASCII/Unicode) or formatted (font, size, style, colour). It is compact in size and easy to edit. Examples: titles, captions, bullet points in a presentation.

2. Graphics (Images) Visual representations such as drawings, photographs, charts, logos and icons. Graphics may be bitmap/raster (made of pixels, e.g. JPEG, PNG, GIF) or vector (made of mathematical lines and curves, e.g. SVG). They make content attractive and help explain ideas quickly. Graphics can be still (static) or animated.

3. Animation A sequence of still images displayed rapidly to create an illusion of movement. It is used to show processes, transitions and effects. Types include 2D and 3D animation. Examples: cartoon characters, loading spinners, animated logos.

4. Audio Sound in the form of speech, music or sound effects. Common formats are WAV, MP3, MIDI and AAC. Audio adds realism and emotion, and is useful for narration, language learning and alerts. It may be speech, music or special effects.

5. Video A moving picture with or without sound — the richest but heaviest component. Formats include MP4, AVI, MKV and MOV. Video is used in movies, tutorials, video conferencing and e-learning. It requires high storage and bandwidth.

6. Interactivity The feature that lets the user control the presentation — clicking, typing, dragging, selecting menus, etc. It distinguishes multimedia from plain television or film. It is provided through hyperlinks, buttons, forms and navigation controls.

Note: Some authors also list hypertext/hypermedia (linked text and media) as a separate component, since linking is what makes multimedia non-linear and interactive.

Conclusion: Text, graphics, animation, audio, video and interactivity together form multimedia. When properly combined, they give an effective, engaging and user-controlled means of communication.

Firewall

A firewall is a network security system (hardware, software, or both) that monitors and controls incoming and outgoing network traffic based on a set of predefined security rules. It acts as a barrier between a trusted internal network and an untrusted external network such as the Internet, allowing only authorized traffic to pass and blocking suspicious or malicious traffic.

Spyware

Spyware is a type of malicious software (malware) that secretly installs itself on a computer and covertly gathers information about the user's activities — such as browsing habits, keystrokes, passwords, and login credentials — and sends it to a third party without the user's knowledge or consent. It may also change browser settings, display unwanted ads, or slow down the system.

Roles of Public and Symmetric Keys

Symmetric key (secret key):

• The same single key is used for both encryption and decryption of data.
• It provides confidentiality by converting plaintext into ciphertext and back, and is very fast, so it is suitable for encrypting large volumes of data (e.g., AES, DES).
• Its main weakness is key distribution: the secret key must be shared securely between sender and receiver before communication, which is difficult over an open network. It also cannot provide authentication or non-repudiation on its own.

Public key (asymmetric key pair — public + private):

• A mathematically related key pair is used: the public key encrypts (or verifies) and the private key decrypts (or signs).
• It solves the key distribution problem, since the public key can be freely published while the private key is kept secret.
• It provides confidentiality (encrypt with receiver's public key), authentication and non-repudiation (sign with sender's private key), and integrity of messages.
• It is slower than symmetric encryption, so in practice it is used to exchange or encrypt a symmetric session key (hybrid approach), while the symmetric key does the bulk data encryption.

Remote Sensing is the science and art of acquiring information about an object, area, or phenomenon without making physical contact with it. This is done by detecting and measuring electromagnetic radiation (reflected or emitted) from the target using sensors mounted on platforms such as satellites, aircraft, drones, or balloons. The recorded data is then processed and interpreted to extract useful information about the Earth's surface, oceans, and atmosphere.

Applications of Remote Sensing:

1. Agriculture: Remote sensing is used to monitor crop health, estimate crop yield, detect crop diseases and pest infestations, and assess soil moisture. Vegetation indices such as NDVI derived from satellite imagery help in precision farming and irrigation planning.

2. Forestry and Land Use Mapping: It helps in mapping forest cover, monitoring deforestation and afforestation, classifying land use/land cover types, and managing forest resources. Multi-temporal satellite data reveal changes in forest area over time.

3. Disaster Management: Remote sensing supports flood mapping, drought monitoring, forest fire detection, earthquake damage assessment, and landslide hazard mapping. It enables rapid damage assessment and relief planning in disaster-affected areas.

4. Urban Planning: Satellite and aerial imagery assist in urban growth monitoring, infrastructure planning, transportation network analysis, and site suitability analysis for development projects.

5. Water Resources Management: It is used to map water bodies, monitor water quality, estimate snow cover and glacier extent, assess groundwater potential, and study watersheds and river basin dynamics.

6. Environmental Monitoring: Remote sensing tracks air and water pollution, monitors coastal erosion, studies climate change impacts, and supports environmental impact assessment and biodiversity conservation.

7. Geology and Mineral Exploration: It aids in geological mapping, identification of rock types, detection of mineral deposits, and study of structural features such as faults and folds.

8. Military and Defense: It is used for surveillance, reconnaissance, target detection, and monitoring of strategic areas.

9. Weather and Climate Studies: Meteorological satellites provide data for weather forecasting, cloud tracking, cyclone tracking, and study of atmospheric phenomena.

10. Oceanography: It helps in measuring sea surface temperature, ocean color, chlorophyll concentration, sea level changes, and monitoring marine ecosystems.

Map projection is the systematic transformation of the curved, three-dimensional surface of the Earth (the ellipsoid or sphere) onto a flat, two-dimensional plane such as a map. Because a curved surface cannot be flattened without distortion, every projection must preserve some properties (area, shape, distance or direction) at the expense of others. It is defined mathematically by a pair of equations relating geographic coordinates (latitude φ, longitude λ) to plane coordinates (x, y):

$x = f(\phi, \lambda), \qquad y = g(\phi, \lambda)$

Common examples are the Mercator, Transverse Mercator, Lambert Conformal Conic and Albers Equal-Area projections. Projections are chosen according to the purpose of the map — conformal projections for navigation, equal-area projections for thematic mapping, and equidistant projections for measuring distances.

Authentication

Authentication is the process of verifying the identity of a user, device or system before granting access to a resource. It answers the question "Are you who you claim to be?" It is performed by checking one or more of three factors:

1. Something you know — password, PIN, passphrase.
2. Something you have — smart card, token, OTP on a mobile phone.
3. Something you are — fingerprint, face, iris or other biometric.

Methods include password-based login, two-factor or multi-factor authentication (combining two or more factors), digital certificates and digital signatures, and biometric verification. Authentication is the first line of defence in GIS and IT systems: it ensures that only authorized users can open a database, edit spatial data or use a web mapping service. It is distinct from authorization, which decides what an authenticated user is allowed to do.

Security awareness

Security awareness is the knowledge, attitude and behaviour of users regarding the protection of information and systems, and the training that develops it. Since most security breaches are caused by human error — weak passwords, phishing emails, careless sharing of data or use of infected USB drives — technical controls alone are not enough. Awareness programmes educate users to:

• use strong, unique passwords and keep them confidential;
• recognize phishing, spam and social-engineering attempts;
• keep software and antivirus updated and back up data regularly;
• follow organizational policies on data sharing, licensing and privacy;
• report suspected incidents promptly.

In the context of GIS, security awareness also covers ethical handling of spatial data, respecting copyright and licensing of maps and satellite imagery, protecting personal location data, and avoiding unauthorized distribution of sensitive maps. Thus authentication provides the technical gate, while security awareness builds the human firewall that keeps that gate effective.

a. Central Processing Unit (CPU)

The Central Processing Unit is the main processing component of a computer that executes program instructions and controls the overall operation of the system. It is often called the brain of the computer, since all data processing and decision-making takes place inside it. On a microcomputer, the CPU is contained in a single silicon chip called a microprocessor.

Main parts:

1. Arithmetic Logic Unit (ALU) — performs all arithmetic operations (addition, subtraction, multiplication, division) and logical operations (comparison, AND, OR, NOT).
2. Control Unit (CU) — fetches instructions from memory, decodes them, and generates control signals that direct the ALU, memory and I/O devices. It maintains the correct sequence of execution.
3. Registers — small, very fast storage locations inside the CPU (e.g. Accumulator, Program Counter, Instruction Register, Memory Address Register) used to hold operands, results and addresses temporarily.
4. Cache memory (in modern CPUs) — a small high-speed memory that stores frequently used instructions and data to reduce the average access time to main memory.

Working cycle: The CPU repeatedly performs the fetch–decode–execute–store cycle. The Program Counter holds the address of the next instruction; the instruction is fetched into the Instruction Register, decoded by the CU, executed by the ALU, and the result is written back to a register or memory. The speed of the CPU is measured in MHz/GHz (clock speed), and its performance also depends on word length, number of cores and cache size. Examples: Intel Core i7/i9, AMD Ryzen, Apple M-series.

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b. Super Computer

A super computer is the fastest, largest and most powerful class of computer available at any given time, designed to perform extremely complex scientific and engineering computations at very high speed. It uses thousands of processors working in parallel and is measured in FLOPS (floating-point operations per second) — modern machines reach petaflops and exaflops.

Characteristics:

• Extremely high processing speed and huge storage capacity.
• Uses parallel processing with a very large number of CPUs/GPUs.
• Very large physical size, high power consumption and requires special cooling and a controlled environment.
• Very expensive to purchase and maintain; operated by large organisations, not individuals.
• Supports multi-user and multi-tasking environment with high reliability.

Uses:

• Weather forecasting, climate modelling and cyclone prediction.
• Nuclear weapon simulation, space research and satellite data analysis.
• Drug discovery, molecular modelling and genome analysis.
• Oil and gas exploration, seismic data processing, aircraft and automobile design (crash simulation).
• Cryptanalysis, artificial intelligence and big-data research.

Examples: Fugaku (Japan), Summit and Frontier (USA), Sunway TaihuLight (China), PARAM Siddhi-AI and PARAM Yuva (India), CRAY series. In Nepal, super-computing facilities are still very limited and such work is generally done through collaboration or cloud services.

Computer Architecture

Computer architecture is the conceptual design and fundamental operational structure of a computer system. It describes those attributes of a computer that are visible to the programmer — the instruction set, the number and types of registers, addressing modes, data formats, memory organisation, and the input/output mechanism — and therefore determines what the computer does when a program is executed.

It is defined by the Von Neumann model, whose essential features are:

• Stored-program concept — both instructions and data are stored in the same memory, so a program can be treated as data and modified by the computer itself.
• A single processing unit (CPU) that executes instructions one after another in sequence.
• A common memory shared by instructions and data, connected to the CPU by a system bus.
• Sequential execution — the fetch–decode–execute cycle is repeated for each instruction.

Computer architecture describes the functional behaviour of the system, whereas computer organisation describes how that architecture is actually built in hardware (the logic circuits, the technology used, the physical connections).

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Block Diagram of a Computer System

        +-------------+      +------------------+      +--------------+
        |  INPUT UNIT |      |   MEMORY UNIT    |      | OUTPUT UNIT  |
        |  Keyboard   |      |  Primary:  RAM,  |      |  Monitor     |
        |  Mouse      |      |  ROM, Cache      |      |  Printer     |
        |  Scanner    |      |  Secondary: HDD, |      |  Plotter     |
        |  Mic, etc.  |      |  SSD, Pen drive  |      |  Speaker     |
        +------+------+      +--------+---------+      +-------+------+
               |                      |                       |
               |                      |                       |
   ============+======================+=======================+============
   |                    SYSTEM BUS  (Data, Address, Control)              |
   ============+======================+=======================+============
               |                      |
               |                      |
        +------+----------------------+-----------------------+
        |                      CPU (Processor)                  |
        |  +-----------+    +-------------+   +--------------+  |
        |  |    ALU    |<-->|  REGISTERS  |<->| CONTROL UNIT |  |
        |  +-----------+    +-------------+   +--------------+  |
        +-------------------------------------------------------+

The arrows show the direction of data/control flow. The three buses form the connecting link between the CPU, memory and the input/output units.

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Explanation of Each Block

1. Input Unit

The input unit accepts data and instructions from the outside world and converts them from human-readable form into binary form that the computer can process.

• Devices: keyboard, mouse, joystick, light pen, touch screen, scanner, microphone, webcam, OMR/OCR/MICR readers.
• Functions:
  1. Accept data and instructions from the user.
  2. Convert them into machine-readable (binary) form.
  3. Supply the converted data to the CPU or to memory for processing.

2. Memory Unit

The memory unit stores instructions, data, intermediate results and final results. It is divided into two main classes.

(a) Primary (main) memory — directly accessible by the CPU:

(b) Secondary (auxiliary) memory — non-volatile, large capacity, cheaper per bit: hard disk, SSD, optical disk, pen drive, magnetic tape. Used for permanent storage of programs and files.

The memory unit is organised as a hierarchy — CPU registers → cache → main memory → secondary storage — where speed decreases and capacity increases as we move down. Memory capacity is measured in bits, bytes, KB, MB, GB and TB. Access may be random (RAM) or sequential (tape).

3. Central Processing Unit (CPU)

The CPU is the brain of the computer; it performs all arithmetic, logic and control operations. It has three main parts.

(a) Arithmetic Logic Unit (ALU) — carries out all arithmetic operations (addition, subtraction, multiplication, division) and all logical operations (AND, OR, NOT, XOR, comparison, shifting). The accumulator holds the intermediate result of these operations.

(b) Control Unit (CU) — the nerve centre. It fetches each instruction from memory, decodes it, and generates the control and timing signals that tell the ALU, memory and I/O units what to do and when. It maintains the correct sequence of operations using the program counter (PC) and instruction register (IR).

(c) Registers — small, very high-speed storage locations inside the CPU used to hold operands and results temporarily:

• PC — address of the next instruction;
• IR — the instruction currently being executed;
• MAR / MBR — memory address and memory buffer registers;
• Accumulator and general-purpose registers — data being processed;
• Flag/status register — condition codes (zero, carry, sign, overflow).

The CPU repeatedly performs the fetch–decode–execute cycle: fetch the instruction whose address is in PC, decode it in the CU, execute it in the ALU, store the result, and increment the PC — unless a branch changes the sequence.

4. Output Unit

The output unit converts the binary results produced by the CPU into human-readable form (text, image, sound, print).

• Devices: monitor/VDU, printer (impact and non-impact), plotter, speaker, projector.
• Functions: receive processed data from the CPU/memory, convert it into a suitable form, and present it to the user. It may be soft copy (screen, speaker) or hard copy (printer, plotter).

5. System Bus (the connections)

The system bus is a group of parallel electrical wires that carries information between the CPU, memory and I/O units. It has three parts:

Working of the connections: When an instruction is to be executed, the CPU places the address of the memory location on the address bus, asserts the memory read line on the control bus, and the memory returns the contents on the data bus. For a write, the CPU puts the address on the address bus, the data on the data bus, and activates the memory write control line. The same mechanism is used for I/O devices, with the control bus selecting memory or I/O. Thus the buses form the common communication path that lets the input unit, memory, CPU and output unit work together as one system.

Database: A database is an organized collection of interrelated data stored in a structured form so that it can be easily accessed, managed, and updated. It stores data in tables (relations) with rows and columns, along with the relationships among the data, so that redundancy is minimized and consistency is maintained. For example, a university database may store records of students, courses, teachers, and marks in related tables.

DBMS: A Database Management System (DBMS) is a collection of programs (software) that acts as an interface between the user/application and the database. It is used to define, create, store, retrieve, update, and control the data of a database, while also providing security, integrity, and concurrent access. Examples: MySQL, Oracle, SQL Server, PostgreSQL, MS Access.

Advantages of DBMS over the flat file system:

1. Control of data redundancy: In a flat file system the same data is repeated in many files (e.g., a student's name in the library file, exam file, and fee file), which wastes space and causes inconsistency. A DBMS stores data in a centralized, normalized form so duplication is minimized.

2. Data consistency: Because data is stored once and shared, an update made at one place is reflected everywhere. In flat files, the same field in different files may hold different values, leading to inconsistent data.

3. Sharing of data: A DBMS allows many users and applications to share the same database simultaneously, whereas flat files are usually designed for one application and are hard to share.

4. Data security: A DBMS provides authorization and access control (user accounts, privileges, views), so only permitted users can read or modify particular data. Flat files rely only on operating-system file permissions, which are coarse and unsafe.

5. Data integrity: A DBMS enforces integrity constraints (primary key, foreign key, domain, NOT NULL, CHECK) so that only valid data enters the database. Flat files have no such automatic checks.

6. Concurrent access and recovery: A DBMS supports multiple transactions at the same time using concurrency control (locking, timestamps) and can restore the database after a crash using logs and backups. Flat files offer no concurrency control and data is easily lost or corrupted.

7. Data independence: In a DBMS the logical and physical structure of data are separated, so changing the storage structure does not require changing application programs. In flat files, the program and file format are tightly coupled, so any change in file layout forces program changes.

8. Backup and recovery facilities: The DBMS provides automatic backup, journaling, and rollback/roll-forward utilities, making recovery simple and reliable, which is absent in flat file systems.

9. Enforcement of standards and improved decision making: A centralized DBMS allows common standards for data names, formats, and formats of reports, and provides query tools and reports that help management take better decisions.

10. Reduced application development and maintenance cost: Because common data and utilities (query language, report generators, forms) are provided, new applications can be built faster and maintained more cheaply than in a flat file environment.

Cryptography

Cryptography is the science and art of transforming a readable message (plaintext) into an unreadable form (ciphertext) so that only the intended recipient can recover the original message, and of designing the techniques and protocols that make this possible. Formally, it is the study of mathematical techniques for providing information security services such as confidentiality, data integrity, authentication, and non-repudiation. A cryptographic system (cryptosystem) is defined by five elements: plaintext, encryption algorithm, key, ciphertext, and decryption algorithm. The basic model is:

$C = E_k(P), \qquad P = D_k(C)$

where $P$ is the plaintext, $C$ the ciphertext, $k$ the key, $E$ the encryption function and $D$ the decryption function.

Significance of cryptography

1. Confidentiality — It keeps sensitive data (passwords, bank details, military messages, medical records) secret from unauthorized users, both while stored and while travelling over insecure networks such as the Internet.
2. Authentication — It verifies the identity of the communicating parties, ensuring a message really comes from the claimed sender and not an impostor.
3. Data integrity — It detects any modification, insertion or deletion of data during transmission using message authentication codes and hash functions.
4. Non-repudiation — Digital signatures prove that a party sent a message, so the sender cannot later deny it; this is essential for e-commerce, contracts and legal transactions.
5. Secure communication over open networks — Protocols such as HTTPS/TLS, VPNs, SSH and Wi-Fi (WPA2) rely on cryptography to protect web browsing, email, remote login and wireless traffic.
6. Foundation of e-commerce and digital economy — Online banking, digital wallets, e-governance and blockchain (cryptocurrency) are all built on cryptographic primitives.
7. Access control and protection of stored data — Encryption of files, passwords (hashing with salt) and full-disk encryption protect data even if the storage device is stolen.
8. National security and defence — Governments use cryptography for classified communications, and cryptanalysis for intelligence.

Difference between symmetric key and public key cryptography

In practice the two are combined in hybrid cryptosystems: public key cryptography distributes the session key, and symmetric cryptography encrypts the actual data (as in TLS/HTTPS).

An operating system (OS) is system software that acts as an interface between the user and the computer hardware, and manages all hardware and software resources of the computer. Any two of its functions are described below.

1. Process Management

The OS manages the execution of all programs (processes) running on the computer. Its main duties are:

• Process creation and termination: It creates processes when a program is executed and removes them when they finish.
• CPU scheduling: When many processes compete for the CPU, the OS decides which process gets the CPU and for how long, using scheduling algorithms such as FCFS, SJF or Round Robin. This ensures fair and efficient use of the CPU.
• Synchronization and communication: It coordinates processes that share data or resources so that they do not conflict with each other.
• Deadlock handling: It detects and recovers from deadlocks, where two or more processes wait endlessly for each other's resources.

Thus, process management keeps the CPU busy and allows many programs to run efficiently at the same time.

2. Memory Management

The OS manages the computer's main memory (RAM), which is a limited and valuable resource. Its main duties are:

• Allocation and deallocation: It allocates memory to programs when they need it and reclaims it when they finish.
• Keeping track of memory: It maintains a record of which parts of memory are in use and by which process, and which parts are free.
• Virtual memory: When RAM becomes full, the OS moves inactive pages of memory to the disk (swapping/paging), giving programs more memory than physically available.
• Protection: It ensures that one process cannot access the memory area of another process, protecting programs from each other.

Thus, memory management makes efficient use of limited main memory and allows multiprogramming.

Conclusion: Besides these two, an OS also performs file management, device management, security and protection, and provides a user interface. Process management and memory management are, however, its most fundamental functions.

Network topology is the physical or logical arrangement of nodes (computers, printers, switches, etc.) and the communication links that connect them in a computer network. It determines how devices are linked and how data flows between them.

Comparison of Bus Topology and Star Topology

Conclusion: Bus topology is simple and cheap but unreliable and hard to troubleshoot, whereas star topology costs more but offers better performance, easier fault isolation and easy expansion, which is why star topology is preferred in modern LANs.

Multimedia is any combination of text, graphics, audio, video, and animation delivered interactively through a computer. Its main components are:

1. Text The most basic element — characters used to convey information. It may be unformatted (plain) or formatted (font, size, style, colour). Text is compact, easy to store and edit, and is used for titles, menus, captions, and body content. Examples: a news article, a help file.

2. Graphics (Images) Digital representations of pictures — drawings, photographs, charts, logos, icons. They are either bitmap/raster (pixels; e.g. JPEG, PNG, GIF — good for photos but lose quality on zooming) or vector (mathematical lines and curves; e.g. SVG — scalable without loss). Graphics make content attractive and explain ideas visually.

3. Audio Sound in digitised form — speech, music, sound effects. Common formats are WAV, MP3, and MIDI. Audio is used in narration, background music, and feedback sounds. It needs compression because raw audio files are large.

4. Video A sequence of moving images played at a frame rate (typically 24–30 fps) to give the illusion of motion. Formats include MP4, AVI, and MPEG. Video is the richest but heaviest component, so codecs (H.264, etc.) are used to compress it. Examples: movies, tutorials, video calls.

5. Animation Rapid display of a series of still images to create movement. It may be 2D or 3D, and frame-based or path-based (tweening). Animation adds life to static content — e.g. a moving logo, a bouncing ball, a cartoon.

6. Interactivity (Hypertext/Hypermedia) The feature that lets the user control the flow — clicking links, buttons, or hotspots. Hypertext links text; hypermedia links text, graphics, audio, and video. This makes multimedia non-linear and user-driven, as in web pages and games.

Summary: Text, graphics, audio, video, and animation are the five media elements, and interactivity binds them into a single interactive system. Together they make multimedia effective for education, entertainment, advertising, and business.

A word processor is application software used to create, edit, format, save and print text-based documents (e.g., MS Word, Google Docs, LibreOffice Writer). Its main features are:

1. Text entry and editing — Typing text and modifying it using insert, delete, overwrite, find, replace, cut, copy and paste.
2. Text formatting — Changing font, size, style (bold, italic, underline), colour, alignment (left, right, centre, justify), line spacing, indentation and paragraph styles.
3. Page layout and printing — Setting margins, page size, orientation (portrait/landscape), headers, footers, page numbers and print preview before printing.
4. Spelling and grammar check — Automatic detection and correction of spelling and grammatical errors, with thesaurus and autocorrect support.
5. Tables, graphics and objects — Inserting tables, pictures, charts, shapes, symbols, equations and hyperlinks into documents.
6. Templates, mail merge and file handling — Using ready-made templates, merging a main document with a data source for bulk letters, and saving documents in various formats (.docx, .pdf, .txt).

These features make word processors far more efficient than ordinary text editors for preparing professional documents.

Remote sensing is the science of acquiring information about the Earth's surface without direct contact, using sensors mounted on satellites, aircraft or drones that record reflected or emitted electromagnetic radiation. Its main application areas are described below.

1. Agriculture and crop management Multispectral and hyperspectral images are used to map crop type and acreage, monitor crop health and vigour through vegetation indices such as NDVI, detect nutrient deficiency, water stress, pest attack and disease, and estimate yield. This supports precision farming, where irrigation, fertilizer and pesticide are applied only where needed.

2. Forestry and biodiversity Remote sensing is used for forest inventory (area, density, species composition), monitoring deforestation and forest degradation, detecting illegal logging and forest fire, and assessing biomass and carbon stock for REDD+ programmes. It also helps map wildlife habitat and track changes in ecosystems.

3. Land use and land cover mapping Satellite data are used to prepare land use/land cover maps, monitor urban expansion and urban sprawl, detect changes over time (change detection), and support town planning, cadastral mapping and infrastructure development.

4. Water resources and hydrology It is applied to map surface water bodies, monitor river channel shifting, floods and drought, estimate snow cover, glacier extent and snowmelt runoff, assess water quality (turbidity, algal blooms) and locate groundwater potential zones.

5. Geology and mineral exploration Remote sensing helps in geological and structural mapping (faults, folds, lineaments), lithological discrimination, and identification of mineral and hydrocarbon bearing zones. Thermal and radar data are used to study volcanoes, earthquakes and land subsidence.

6. Disaster management Satellite images are used for hazard mapping (landslide, flood, earthquake, cyclone), rapid damage assessment after a disaster, and for early warning, relief planning and post-disaster rehabilitation.

7. Environment and climate studies It is used to monitor air and water pollution, deforestation, desertification, glacier retreat, sea level rise, and land and sea surface temperature, providing key inputs to climate change models.

8. Meteorology and weather forecasting Weather satellites provide cloud cover, cloud top temperature, precipitation, wind and humidity data used in numerical weather prediction and cyclone tracking.

9. Ocean and coastal applications Remote sensing is used to measure sea surface temperature, ocean colour and chlorophyll (fishery potential), map coastal erosion and sedimentation, and monitor coral reefs and mangroves.

10. Urban, engineering and military applications It supports site selection for dams, roads and airports, route alignment, topographic and DEM generation, and military surveillance, target detection and reconnaissance.

Conclusion Thus remote sensing has wide and diverse applications ranging from resource inventory and environmental monitoring to disaster management and national security, making it an indispensable tool for planning and sustainable development.

WWW (World Wide Web)

The World Wide Web (WWW) is a system of interlinked hypertext documents and multimedia content that are accessed over the Internet using browsers. It was invented by Tim Berners-Lee in 1989 at CERN. The WWW works on the client–server model: a web browser (client) sends a request to a web server, which returns the requested web page. It uses three core technologies:

• HTML – to structure and format web pages.
• HTTP/HTTPS – the protocol for transferring web pages between client and server.
• URL – to uniquely identify the address of each resource on the web.

Each web page is identified by a URL (e.g., https://www.tu.edu.np) and pages are linked through hyperlinks, allowing users to navigate from one page to another. The WWW is the most widely used Internet service, providing information, e-commerce, email, social networking, e-learning, etc. Note that the WWW is only one service of the Internet — the Internet is the underlying network, while the Web is a service running on it.

TELNET

TELNET (Terminal Network) is a standard TCP/IP application-layer protocol that allows a user to log in to a remote computer over the Internet and work on it as if sitting at its local terminal. It works on the client–server model and uses TCP port 23 for communication. The user runs a Telnet client, connects to the remote host by its IP address or domain name, and after authentication (username and password) gets a virtual terminal on the remote machine. Commands typed by the user are sent to the remote host, executed there, and the results are returned to the local terminal. It is mainly used by network administrators for remote login, configuration and management of servers, routers and switches. Its major drawback is that all data, including passwords, is sent in plain text, so it is insecure; hence it has largely been replaced by SSH (Secure Shell), which provides encrypted remote login.

FTP (File Transfer Protocol)

FTP is a standard TCP/IP application-layer protocol used to transfer files between a local computer and a remote server over a network. It also follows the client–server model and uses two TCP connections:

• Control connection on port 21 – for sending commands and receiving replies.
• Data connection on port 20 (or a negotiated port) – for the actual transfer of file contents.

FTP supports two transfer modes: ASCII mode for text files and binary/image mode for programs, images, audio and video files. Files can be transferred in both directions — upload (local to remote) and download (remote to local). It supports anonymous FTP, where any user can log in with the username anonymous and an email address as password to access public files. FTP is widely used for uploading website files to a web server and for downloading software. Like Telnet, ordinary FTP sends data in plain text, so SFTP (Secure FTP) or FTPS is used where security is required.

GIS (Geographic Information System) is a computer-based system designed to capture, store, retrieve, manipulate, analyse, and display spatially referenced (geographic) data. It links locational information (where things are) with attribute information (what things are like), enabling map production, spatial query, and decision support.

Difference between spatial and non-spatial data

Use of remote sensing in water resources management

1. Rainfall and precipitation estimation – Satellites (e.g., TRMM, GPM, INSAT) provide rainfall estimates over ungauged and inaccessible mountain basins where rain gauges are scarce.
2. Snow cover and snowmelt runoff – Optical and microwave sensors map snow-covered area and snow water equivalent, which is used to forecast seasonal snowmelt runoff in Himalayan rivers.
3. Reservoir and lake monitoring – Satellite imagery measures water spread area, storage volume changes, sedimentation and shoreline shifts, helping reservoir operation and planning.
4. Flood mapping and monitoring – SAR (e.g., Sentinel-1) and optical data delineate flood extent, inundation depth and damage, supporting early warning and relief planning.
5. Drought assessment – Vegetation indices (NDVI), land surface temperature and evapotranspiration products detect moisture stress and drought severity.
6. Groundwater and soil moisture – GRACE gravity data and microwave radiometry estimate groundwater depletion and soil moisture for irrigation scheduling.
7. Water quality monitoring – Spectral reflectance of water bodies detects turbidity, suspended sediment, chlorophyll-a and algal blooms in lakes and rivers.
8. Watershed and irrigation planning – DEMs from remote sensing give slope, drainage network and catchment boundaries used in watershed management, dam siting and canal layout.
9. Evapotranspiration and irrigation demand – Thermal and optical data (SEBAL/METRIC models) estimate crop water use for efficient irrigation management.
10. Glacier and river morphology studies – Repeated imagery tracks glacier retreat, river channel migration and bank erosion, supporting long-term water resource planning.

Cryptography is the science and art of transforming a plain, readable message (plaintext) into an unreadable form (ciphertext) using mathematical techniques and a secret key, so that only the intended receiver can recover the original message. Formally, a cryptosystem is a five-tuple $(P, C, K, E, D)$ where $P$ is the set of plaintexts, $C$ the set of ciphertexts, $K$ the set of keys, $E$ the encryption function and $D$ the decryption function such that $D_k(E_k(P)) = P$.

Why cryptography is required

1. Confidentiality — It keeps data secret from unauthorized users. Encryption ensures that even if data is intercepted, it cannot be read without the key.
2. Authentication — It verifies the identity of the sender/receiver, confirming that a message really came from the claimed party and not from an impostor.
3. Integrity — It detects any modification, insertion or deletion of data during transmission, so the receiver knows the message has not been tampered with.
4. Non-repudiation — It provides proof of origin so that a sender cannot later deny having sent a message (achieved through digital signatures).
5. Access control and protection of stored data — Passwords, PINs, files and databases are stored in encrypted/hashed form so that even system administrators or attackers who gain access cannot misuse them.
6. Secure communication over untrusted networks — The Internet, wireless links and e-mail are open channels; cryptography (SSL/TLS, HTTPS, VPN) makes them safe for banking, e-commerce and messaging.

Symmetric key cryptography

In symmetric key cryptography (also called secret key or private key cryptography), the same single key is used both for encryption and for decryption. The sender and receiver must share this key secretly before communication begins. The general model is:

$C = E_k(P), \qquad P = D_k(C)$

where $k$ is the shared secret key. Because only one key is used, the algorithm is simple and fast, which makes it suitable for encrypting large volumes of data. Its main weakness is key distribution and management: if $n$ users want to communicate pairwise, $\frac{n(n-1)}{2}$ keys are needed, and if the key is lost or leaked, the whole security is broken. It also cannot provide non-repudiation by itself. Common symmetric algorithms are DES, 3DES, AES, Blowfish, RC4 and IDEA.

Example: Caesar cipher

The Caesar cipher is the simplest symmetric key cipher. Each letter of the plaintext is shifted forward in the alphabet by a fixed number of positions, and that shift value is the secret key. For a key $k = 3$:

$E_k(x) = (x + k) \bmod 26, \qquad D_k(y) = (y - k) \bmod 26$

where $x$ and $y$ are the numeric positions of the letters ($A = 0, B = 1, \dots, Z = 25$).

Let the plaintext be "CAT" and the key be $k = 3$.

So the ciphertext is "FDW".

Decryption with the same key $k = 3$:

The original plaintext "CAT" is recovered. This shows the essential property of symmetric cryptography: the same key $k = 3$ was used for both encryption and decryption. In practice, modern symmetric ciphers such as AES use the same principle but with a 128-bit key and complex substitution–permutation rounds, making brute-force attack infeasible.

Basic Characteristics of a Computer (4 marks)

1. Speed — A computer works at an extremely high speed, performing millions of instructions per second. The unit of speed is microsecond, nanosecond or picosecond.
2. Accuracy — Results are 100% accurate; errors occur only due to wrong input data or wrong instructions (GIGO — Garbage In Garbage Out).
3. Diligence — A computer never gets tired, bored or distracted. It can work continuously for hours with the same efficiency.
4. Versatility — The same machine can do many different jobs (typing, accounting, designing, playing music) by simply changing the program.
5. Storage Capacity — It can store a huge amount of data and instructions in its memory and retrieve them instantly.
6. Automatic — Once a program and data are fed in, the computer carries out the whole sequence of operations automatically without human intervention.
7. No Intelligence / No IQ — A computer has no thinking power of its own; it cannot take decisions on its own. It only follows the instructions given by the user.
8. No Feeling / Emotion — It has no feelings, emotions or senses, so it is unaffected by fatigue, tension or personal bias.
9. Reliability — It gives consistent results for the same input every time.
10. Cost-effective — Although the initial cost is high, the per-work cost becomes very low because of its speed and accuracy.

Difference between Analog and Digital Computers (6 marks)

Note: A hybrid computer combines features of both — it accepts analog signals but processes them digitally. Examples: ECG machine, digital petrol pump, flight simulator, patient-monitoring system in hospitals.

Process Management by the Operating System

A process is a program in execution. A program by itself is a passive entity stored on disk; when it is loaded into memory and given a CPU to run, it becomes a process. Process management is the set of activities by which the operating system creates, schedules, controls, and terminates processes so that the CPU is shared efficiently among many programs.

The main functions of process management are described below.

1. Process creation and termination The OS creates a process when a program is launched (by loading its code and data into memory and setting up a Process Control Block). It also provides ways to terminate a process when it finishes or is killed. In many systems a process can create child processes (e.g., fork() in UNIX).

2. Maintaining the Process Control Block (PCB) For every process the OS keeps a data structure called the PCB, which stores:

• Process ID (PID) and parent PID
• Program counter and CPU registers (the process state)
• CPU scheduling information (priority, time used)
• Memory-management information (base/limit, page tables)
• Accounting information and I/O status

The PCB is the record the OS uses to save and restore a process.

3. Process scheduling The OS decides which process should use the CPU and for how long. This involves:

• Long-term scheduler – selects which jobs are admitted into the ready queue.
• Short-term scheduler (CPU scheduler) – selects the next process from the ready queue for the CPU.
• Medium-term scheduler – swaps processes in and out of memory to control the degree of multiprogramming.

Scheduling algorithms such as FCFS, SJF, Round Robin, and Priority scheduling are used to meet goals like maximum CPU utilization, fairness, and minimum waiting time.

4. Process state management A process passes through states: new → ready → running → waiting (blocked) → terminated. The OS moves a process from one state to another. For example, when a running process requests I/O it goes to the waiting state; when I/O completes it returns to ready; when its time slice expires it goes back to ready.

5. Context switching When the CPU switches from one process to another, the OS saves the state (registers, program counter) of the old process into its PCB and loads the saved state of the new process. This is called a context switch. It lets many processes share one CPU, though the switch itself takes some overhead time.

6. Inter-process communication and synchronization Processes often need to exchange data or coordinate their actions. The OS provides mechanisms such as shared memory, message passing, semaphores, and monitors to allow communication and to prevent problems like race conditions and deadlock.

7. Resource allocation and protection The OS allocates CPU time, memory, files, and I/O devices to processes and ensures that one process cannot wrongly access the resources of another, thus providing protection and isolation.

Conclusion In short, process management means the OS creates processes, keeps track of their state through the PCB, schedules them on the CPU, handles their state transitions and context switches, and provides communication and protection among them. This gives efficient, fair, and safe sharing of the CPU and other resources.

Network Topologies

A network topology is the physical or logical arrangement of nodes (computers, switches, routers) and communication links in a computer network. The choice of topology affects cost, performance, reliability, and ease of expansion. The main topologies are described below.

1. Bus Topology

All nodes are connected to a single common backbone cable (the bus), with terminators at both ends.

• Advantages: Simple, requires least cable, cheap for small networks.
• Disadvantages: A single break in the backbone disables the whole network; difficult to isolate faults; performance degrades as nodes increase due to collisions.

2. Star Topology

Every node is connected by a separate link to a central device such as a hub or switch.

• Advantages: Easy to install and manage; failure of one link does not affect others; easy fault isolation and expansion.
• Disadvantages: The central device is a single point of failure; more cable is required than in bus topology.

3. Ring Topology

Each node is connected to exactly two neighbours, forming a closed loop. Data travels in one direction (or both in a dual ring), usually with a token.

• Advantages: No collisions in token ring; predictable performance; every node acts as a repeater.
• Disadvantages: Failure of one node or link can break the entire ring; adding or removing nodes disrupts the network.

4. Star-Bus (Tree) Topology

Multiple star networks are connected to a common bus backbone. It is a hierarchical extension of bus and star topologies.

• Advantages: Scalable; suitable for large organisations; faults in one branch do not affect others.
• Disadvantages: Heavy cabling; the backbone and root device are critical points of failure.

5. Mesh Topology

Every node is connected to every other node by a dedicated link. In a full mesh with n nodes, the number of links is:

$\text{Links} = \frac{n(n-1)}{2}$

• Advantages: Very high fault tolerance and reliability; no traffic congestion; privacy and security are high.
• Disadvantages: Very expensive and difficult to install due to large cabling and port requirements.

6. Star Topology Variant — Hybrid Topology

A hybrid topology combines two or more different topologies (for example, star-ring or star-mesh) to gain the advantages of each.

• Advantages: Flexible, reliable, and scalable.
• Disadvantages: Complex design and high implementation cost.

7. Wireless Topologies

In wireless networks, nodes communicate through radio signals. Common forms are infrastructure mode (nodes connect via an access point) and ad-hoc mode (nodes communicate directly).

Comparison Summary

Conclusion: Bus and ring are simple but fragile; star is the most widely used in LANs; mesh offers the highest reliability at high cost; and hybrid topologies are used in large, complex networks where flexibility and fault tolerance are essential.

Uses of the Internet

The internet is a global network of interconnected computers that allows users to share information and communicate worldwide. Its major uses are:

1. Communication — Email, instant messaging, video conferencing (Zoom, Google Meet) and social media (Facebook, Instagram) allow people to exchange messages, voice and video across the world instantly and at low cost.

2. Information search and education — Search engines (Google), online encyclopedias (Wikipedia), e-books, online journals and e-learning platforms (Coursera, YouTube) give instant access to knowledge, notes and lectures. Students can attend virtual classes and download study materials.

3. E-commerce and online banking — Buying and selling goods and services online (Amazon, Daraz), online payment (eSewa, Khalti), mobile banking, bill payment and fund transfer without visiting a bank or shop.

4. Entertainment — Streaming music and video (YouTube, Netflix), online games, live sports and news, and downloading movies and songs.

5. Business and employment — Advertising products, online marketing, video meetings with clients, freelancing and remote (work-from-home) jobs, and job search through portals.

6. Cloud services and file sharing — Storing and sharing data on Google Drive, Dropbox and OneDrive, so files can be accessed from any device, anywhere.

7. Government and public services — Online application for citizenship, passport, exam results, tax filing, and access to government notices and forms.

8. Social networking — Staying in touch with friends and relatives, forming interest groups, and sharing ideas, photos and opinions.

Two examples:

• Example 1: E-learning — A student in a remote village of Nepal uses YouTube and Google Classroom to watch lectures and submit assignments, so education is no longer limited to a physical classroom.
• Example 2: Online banking (eSewa/Khalti) — A person pays electricity bills, mobile recharge and college fees from a mobile phone within minutes, saving the time and cost of travelling to the bank or counter.

Difference between Database and Data Warehouse

Need of a Data Mart

A data mart is a small, subject-specific subset of a data warehouse, built for the needs of a particular department or group of users. Its need arises because:

1. Faster and cheaper implementation — A full enterprise warehouse takes years and huge cost; a data mart can be built in weeks or months at low cost.
2. Departmental focus — Each department (sales, finance, HR) needs only its own subject area, so a focused data mart gives relevant data without irrelevant clutter.
3. Easier access and better performance — Since it holds less data, queries run faster and users find the required information easily.
4. Local control and ownership — The department can define, maintain and modify its own data mart without depending on the central IT warehouse team.
5. Better security — Sensitive departmental data is isolated and visible only to authorized users of that department.
6. Stepping stone to a warehouse — Data marts built bottom-up can later be integrated to form the complete enterprise data warehouse.

Uses of multimedia (2 marks)

Multimedia combines text, graphics, audio, video and animation into one interactive presentation. Its main uses are:

• Education and training — e-learning packages, CBT (computer-based training) and virtual labs make learning interactive.
• Entertainment — games, movies, music videos and streaming services.
• Business and advertising — product presentations, kiosks, video conferencing and e-commerce catalogues.
• Communication — video calls, teleconferencing and webinars.
• Medicine and engineering — simulation, surgical training and CAD visualisation.
• Public information — digital museums, tourism guides and information kiosks at airports and stations.

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Graphics (4 marks)

Graphics are the non-text pictorial elements of a multimedia application — drawings, charts, photographs, icons, logos and diagrams — used to convey information visually.

Types:

Uses: illustrate concepts, present data as charts/graphs, build user interfaces (buttons, icons), and improve the visual appeal of a title or web page.

Tools: Adobe Photoshop, CorelDRAW, Adobe Illustrator, MS Paint.

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Animation (4 marks)

Animation is the technique of creating an illusion of movement by displaying a sequence of still images (frames) rapidly, one after another. Persistence of vision makes the eye perceive them as continuous motion; typically 24–30 frames per second are needed.

Types:

• 2D animation — objects have length and width only (e.g. cartoons such as Tom and Jerry).
• 3D animation — objects have length, width and depth, modelled in three axes (e.g. Toy Story, Frozen).
• Cel / frame-by-frame animation — every frame is drawn separately.
• Path animation — an object is moved along a defined path.
• Morphing — one shape is gradually transformed into another.
• Stop-motion — real objects are photographed frame by frame.

Uses: cartoon films, advertisements, computer games, web banners, simulation and e-learning modules.

Tools: Adobe Animate (Flash), Blender, Maya, 3ds Max, After Effects.

a. System Software

System software is a class of computer programs that manage and control the hardware of a computer system and provide a platform on which application software runs. It acts as an interface between the user/application programs and the underlying hardware. Unlike application software, which performs specific user-oriented tasks, system software is general-purpose and is essential for the computer to function at all.

Main components:

• Operating System — the core system software (e.g., Windows, Linux, macOS). It manages the CPU, memory, storage, and I/O devices, and provides services such as process scheduling, memory management, file management, and security.
• Language Translators — compilers, interpreters, and assemblers that convert high-level or assembly source code into machine code.
• Device Drivers — programs that let the OS communicate with specific hardware such as printers, keyboards, and graphics cards.
• Utility Programs — tools for maintenance and housekeeping, e.g., disk defragmenters, antivirus, backup tools, and file managers.
• Loaders and Linkers — load executable programs into memory and link separate object modules into a single program.

Functions: resource management, memory and process management, input/output control, error detection, file management, and providing the user interface (CLI or GUI).

Characteristics: written mostly in low-level or system programming languages (C, assembly), close to hardware, memory-resident or loaded at boot time, and usually supplied along with the computer rather than purchased separately.

Conclusion: System software is the foundation of any computer system — without it, application software cannot execute and hardware cannot be utilized efficiently.

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b. Security Threat

A security threat is any circumstance, event, or action that has the potential to cause harm to a computer system by compromising the confidentiality, integrity, or availability (CIA) of its data and resources. Threats may be accidental (e.g., natural disaster, human error) or intentional (e.g., attacks by hackers).

Major types of security threats:

1. Malware — malicious software designed to damage or gain unauthorized access to a system. It includes:

   • Virus — attaches to files and spreads when they are executed.
   • Worm — self-replicating program that spreads across networks.
   • Trojan Horse — disguises itself as useful software but performs harmful actions.
   • Ransomware — encrypts data and demands payment for its release.
   • Spyware / Keyloggers — secretly record user activity and keystrokes.

2. Phishing — fraudulent emails, messages, or websites that trick users into revealing passwords, bank details, or other sensitive information.

3. Denial of Service (DoS/DDoS) — flooding a server or network with traffic so that legitimate users cannot access its services.

4. Password Attacks — brute force, dictionary, or credential-stuffing attacks aimed at guessing or stealing login credentials.

5. Man-in-the-Middle (MITM) Attack — an attacker secretly intercepts and possibly alters communication between two parties.

6. SQL Injection — inserting malicious SQL code into input fields to access or destroy database contents.

7. Social Engineering — manipulating people psychologically to disclose confidential information.

8. Physical Threats — theft of hardware, unauthorized physical access, fire, flood, or power failure.

Countermeasures: use of antivirus and firewall software, strong and regularly changed passwords, multi-factor authentication, data encryption, timely software updates and patches, regular backups, user awareness training, and physical security of equipment.

Conclusion: Since threats are constantly evolving, security must be treated as a continuous process combining technical controls, proper policies, and educated users.