Computer Fundamentals and Applications

Logical system architecture: Logical system architecture is the layered, conceptual view of a computer system that shows how its parts relate to each other, without describing the physical details. Each layer uses the services of the layer below it and offers services to the layer above:

1. Hardware layer: the physical devices (CPU, memory, I/O devices).
2. System software layer (OS, device drivers, utilities, translators): manages hardware and gives services to the layers above.
3. Application software layer: programs that solve user problems (word processors, browsers).
4. User layer: the end users who interact with the applications.

This layering hides complexity: a user need not know how the hardware works.

Role of system software: System software is a set of programs that control and manage the computer hardware and provide a platform for running application software.

• Resource management: Allocates CPU time, memory, files and I/O devices to different programs.
• Interface between user/application and hardware: Gives a GUI or command line and system calls.
• Program translation: Compilers, interpreters and assemblers convert source code into machine code.
• Device control: Device drivers let the OS communicate with printers, disks, keyboards, etc.
• System maintenance and efficiency: Utility programs (antivirus, disk cleanup, backup, file compression) keep the system healthy.
• Loading and linking: Loaders and linkers prepare programs for execution; bootstrap loader starts the system.
• Security and error handling: Controls access, detects errors and recovers from them.

Examples: Operating systems (Windows, Linux, Android), language translators (GCC compiler, Python interpreter), device drivers, utility programs and firmware/BIOS.

GPS (Global Positioning System): GPS is a satellite-based navigation system, owned by the USA, made of a network of about 24-32 satellites orbiting the earth. A GPS receiver calculates its exact position (latitude, longitude, altitude), speed and time by measuring the signals from at least four satellites (trilateration). It is used in vehicle and mobile navigation, tracking, surveying, aviation, mapping, and in military use.

Difference between impact and non-impact printers:

Network topology: Network topology is the geometrical arrangement (layout) of the devices (nodes) and links in a computer network. It can be physical (actual layout) or logical (data flow).

1. Bus topology: All nodes are connected to a single common backbone cable, with terminators at the ends.

• Advantages: cheap, easy to install, needs less cable.
• Disadvantages: if the backbone fails the whole network fails; slow with heavy traffic; difficult fault finding.

2. Star topology: All nodes are connected to a central hub or switch.

• Advantages: easy to install and add nodes; failure of one node does not affect others; easy fault detection.
• Disadvantages: the central device is a single point of failure; more cable and cost.

3. Ring topology: Each node is connected to exactly two neighbours, forming a closed loop; data moves in one direction (token passing).

• Advantages: equal access, no collision, performs well under load.
• Disadvantages: failure of one node or cable breaks the ring; difficult to add nodes; troubleshooting is hard.

4. Mesh topology: Every node is connected to every other node (n(n-1)/2 links for n nodes).

• Advantages: very reliable and fault tolerant; secure; direct communication.
• Disadvantages: costly, with too much cabling; complex to install.

5. Tree (hierarchical) topology: Groups of star networks connected to a central bus backbone.

• Advantages: scalable, easy fault finding.
• Disadvantages: backbone failure splits the network; costly.

6. Hybrid topology: A combination of two or more topologies; flexible and reliable but complex and costly.

Internet of Things (IoT) is a network of physical objects (things) embedded with sensors, software and network connectivity that collect and exchange data over the Internet, usually without human intervention.

Working: sensors collect data, which is sent through a network (Wi-Fi, Bluetooth, Zigbee, cellular) to a cloud or gateway, where it is processed and an action is taken or shown to the user through an app.

Components: sensors/actuators, connectivity, data processing (cloud/edge), and user interface.

Applications:

• Smart home (smart lights, thermostats, CCTV).
• Wearables and healthcare monitoring.
• Smart agriculture (soil moisture sensors).
• Smart cities (traffic, street lighting, waste management).
• Industrial IoT and vehicle tracking.

Advantages: automation, efficiency, real-time monitoring, saving of cost and energy.

Challenges: security and privacy risks, device compatibility, power consumption and dependence on network.

Firmware is permanent software programmed into a hardware device's non-volatile memory (ROM, EEPROM or flash) that controls how the device works. It lies between hardware and software.

Characteristics:

• Stored in non-volatile memory, so it is kept when power is off.
• Provides low-level control of hardware and starts the device.
• Can be updated ("flashing") in modern devices.

Examples: BIOS/UEFI in a motherboard, firmware in a router, printer, hard disk, digital camera, washing machine, smart TV and mobile phones.

Importance: it makes hardware work correctly, allows bug fixes and new features by updates, and performs the start-up process (BIOS loads the OS).

A computer evolved from simple mechanical counting aids to today's intelligent machines. Its development is usually described in terms of generations, each marked by a major change in the hardware technology used.

Early developments: The abacus (counting frame), Napier's bones, Pascal's calculator (1642), Leibniz's calculator, and Charles Babbage's Difference Engine and Analytical Engine (1830s) led the way. Babbage is called the "father of the computer", and Ada Lovelace wrote the first program idea. Later Howard Aiken's Mark I and ENIAC (1946) appeared.

Latest (fifth) generation: The fifth generation is based on Ultra Large Scale Integration (ULSI) with millions or billions of transistors on one chip, and focuses on Artificial Intelligence. Its main features are:

• Machine learning, expert systems, natural language processing and speech recognition.
• Parallel processing and multi-core processors; very high speed and large memory.
• Use of cloud computing, IoT, big data and portable devices (laptops, smartphones, tablets).
• Research into quantum computing and nanotechnology.
• Easy human interaction through voice, touch and gesture.

Examples include AI assistants (Siri, Alexa), self-driving systems and robots.

System: A system is a set of interrelated components that work together in an organised way to achieve a common goal. A computer system is made of hardware, software, data and people that together take input, process it, and produce output.

Architecture of a digital computer: A digital computer works on discrete (binary) data and is built from the following sub-systems (the von Neumann model):

1. Input unit: Accepts data and instructions from the user and converts them to binary form the computer understands. Examples: keyboard, mouse, scanner, microphone.
2. Central Processing Unit (CPU): The brain of the computer, which has three parts:
   • Arithmetic Logic Unit (ALU): Performs arithmetic (+, -, x, /) and logical (AND, OR, NOT, comparison) operations.
   • Control Unit (CU): Fetches instructions from memory, decodes them, and directs and coordinates all other units; it does not process data itself.
   • Registers: Very fast small storage inside the CPU holding data, addresses and instructions currently being processed (e.g. PC, IR, accumulator).
3. Memory unit: Stores data and instructions before, during and after processing.
   • Primary memory (RAM, ROM, cache) is fast and directly accessible by the CPU.
   • Secondary memory (hard disk, SSD, DVD, pen drive) is large, permanent storage.
4. Output unit: Converts the binary results into a human-readable form. Examples: monitor, printer, speaker, plotter.
5. Buses (interconnection): Data bus, address bus and control bus carry data, memory addresses and control signals between the units.

Working: Data and program enter through the input unit and are stored in memory. The control unit fetches an instruction, decodes it, and the ALU executes it. Results are stored in memory and sent to the output unit. Results and data can be saved in secondary storage.

Input unit --> [ CPU: CU + ALU + Registers ] <--> Memory unit --> Output unit
                         ^                              |
                         +---- Secondary storage -------+

Computer software: Software is a collection of programs, procedures, and related data that tells the computer hardware what to do and how to do it. It is intangible: it cannot be touched but is stored on and run by hardware. The two main categories are system software and application software.

Differences between system and application software:

Firmware: Firmware is permanent software programmed into the read-only or flash memory (ROM, EEPROM, flash) of a hardware device. It controls the basic functions of the device, sits between hardware and higher-level software, and is retained when power is off.

• It contains low-level instructions for starting and operating the device (e.g. BIOS/UEFI that boots a PC).
• It can be updated ("flashing") to fix bugs or add features.
• Examples: BIOS/UEFI, router firmware, firmware in a TV remote, printer, digital camera, washing machine and smartphone.

Middleware: Middleware is software that lies between the operating system and the application programs (often on different machines) and enables them to communicate and exchange data. It acts as a "software glue" in distributed systems.

• It hides the differences in hardware, operating systems and network protocols from application developers.
• It provides services such as messaging, authentication, data access, API management and transaction handling.
• Examples: database middleware like ODBC/JDBC, message-oriented middleware (RabbitMQ, Kafka), web application servers (Tomcat), CORBA, object request brokers.

In short, firmware is embedded software controlling hardware, while middleware connects applications and services in a network.

Ways a computer receives data: A computer receives input in several ways:

• Typing / keying: keyboard (text, numbers, commands).
• Pointing and selecting: mouse, touchpad, trackball, touch screen, joystick, light pen.
• Scanning and optical reading: scanner, barcode reader, OMR, OCR, MICR.
• Image and video capture: digital camera, webcam.
• Voice / audio capture: microphone with speech recognition.
• Sensors and biometrics: fingerprint and iris scanners, motion and temperature sensors.
• Storage media and network: data read from a disk, pen drive, or received from another computer over a network.

Mouse: A mouse is a hand-held pointing input device that controls the movement of a pointer (cursor) on the screen.

• Types: mechanical (ball), optical (LED light), laser and wireless/Bluetooth mouse.
• Working: movement over a surface is detected by the ball rollers or by an optical sensor, converted to electrical signals and sent to the computer to move the pointer. Buttons (left, right) and the scroll wheel send click and scroll signals.
• Use: clicking, double clicking, dragging, dropping, selecting, and in GUI and graphics designing. It is easy to use and fast for GUI work but needs a flat surface and is not suitable for typing text.

Microphone: A microphone is an input device that converts sound waves (analog) into electrical signals, which a sound card converts into digital form.

• Working: sound waves vibrate a thin diaphragm, and this vibration is converted to an electrical signal (by a coil/magnet in a dynamic microphone or a capacitor in a condenser microphone).
• Uses: voice recording, video conferencing, online meetings, voice commands, speech-to-text and gaming.

A speech recognition device (speech-to-text system) converts spoken words into text or computer commands. It consists of a microphone, a sound card, and recognition software.

Working steps:

1. Audio capture: The microphone picks up the speaker's voice (analog sound waves) and converts it into an electrical signal.
2. Digitisation: The sound card's analog-to-digital converter (ADC) samples the signal and converts it into digital data.
3. Pre-processing: Background noise is filtered out and the signal is normalised and split into small frames.
4. Feature extraction: The software extracts features such as frequency and pitch from each frame to find the phonemes (the basic units of sound).
5. Pattern matching: The phonemes are compared with an acoustic model and a stored vocabulary/dictionary using algorithms such as Hidden Markov Models or neural networks. The most likely words are selected.
6. Language model: A language model uses grammar and word probability (context) to choose the correct word sequence (e.g. "write" or "right").
7. Output: The recognised text is displayed or the matching command is executed.

Types: speaker-dependent (needs training for a particular voice) and speaker-independent (works for any voice).

Uses: voice typing, voice assistants (Siri, Google Assistant), phone banking, controlling devices for physically disabled users, and transcription.

Differences between monitor and projector:

Applications of sound card: A sound card is an expansion card (or chip) that converts digital data into sound and sound into digital data.

• Playing music, movies, games and system sounds through speakers or headphones.
• Recording voice and music through a microphone.
• Video conferencing and voice chat; speech recognition.
• Audio/video editing and music production (MIDI).

Applications of video card (graphics card): It has its own processor (GPU) and memory (VRAM) and produces the images sent to the monitor.

• Displaying high-resolution graphics and video smoothly.
• 3D gaming and animation, video editing and rendering.
• CAD/CAM and graphic design.
• Supporting multiple monitors; also GPU computing such as machine learning and crypto mining.

Memory: Memory is the part of a computer that stores data, instructions and results, either temporarily or permanently. It is measured in bytes (KB, MB, GB, TB). Memory is divided into primary and secondary memory.

Primary memory (main memory): This memory is directly accessed by the CPU. It is fast, but costly and has limited capacity. The types are:

1. RAM (Random Access Memory): Volatile, read/write memory which holds the programs and data currently in use; its contents are lost when power is off.
   • SRAM (static RAM): faster, no refresh needed, costly, used for cache.
   • DRAM (dynamic RAM): uses capacitors, needs periodic refresh, cheaper, used as main memory (SDRAM, DDR).
2. ROM (Read Only Memory): Non-volatile memory that holds permanent instructions like the BIOS/bootstrap program.
   • PROM: programmable once by the user.
   • EPROM: erased by ultraviolet light and reprogrammed.
   • EEPROM/flash: erased electrically and rewritten.
3. Cache memory: Very fast small memory between CPU and RAM that keeps frequently used data and instructions to reduce access time (L1, L2, L3).
4. Registers: The fastest, smallest memory inside the CPU.

Storage device: A storage device is a hardware component used to store, port and extract data and programs, either temporarily or permanently, e.g. RAM, hard disk, CD.

Secondary storage devices: These are non-volatile, high-capacity, low-cost devices that keep data permanently. They are not directly accessed by the CPU (data is first moved to RAM) and are slower than primary memory.

1. Magnetic storage
   • Hard Disk Drive (HDD): rotating platters coated with magnetic material, read/written by heads; capacity from hundreds of GB to many TB; used as the main storage of a computer.
   • Floppy disk: small removable disk (1.44 MB), now obsolete.
   • Magnetic tape: sequential access, cheap and large; used for backup and archiving.
2. Optical storage: data is read/written by a laser beam.
   • CD-ROM / CD-R / CD-RW: about 700 MB.
   • DVD: 4.7 GB (single layer) up to 8.5 GB or more.
   • Blu-ray disc: 25 GB or more, for HD video.
3. Solid-state / flash storage: no moving parts, fast, durable.
   • SSD (Solid State Drive).
   • USB pen drive, memory card (SD card).
4. Cloud storage: data stored on remote servers over the internet (Google Drive, OneDrive).

Characteristics: large capacity, non-volatile, cheap per byte, portable (many types), slower than RAM.

Basic elements of a communication system:

1. Sender (source): the device that creates and sends the message (e.g. a computer or phone).
2. Message: the information (text, audio, video, image, data) to be communicated.
3. Transmission medium (channel): the physical path over which the message travels.
4. Receiver (destination): the device that receives the message.
5. Protocol: the set of rules agreed on by sender and receiver for communication (e.g. TCP/IP, HTTP).

Data transmission media:

A. Guided (wired) media

• Twisted pair cable: two insulated copper wires twisted together; UTP and STP; cheap and easy to install, used in LANs and telephones; limited distance (100 m) and prone to noise.
• Coaxial cable: central copper conductor, insulation, shield and outer cover; better shielding and bandwidth than twisted pair; used in cable TV and older networks.
• Optical fibre cable: thin glass/plastic strands that carry data as light pulses; very high speed and bandwidth, immune to electromagnetic interference, secure, long distance; but costly and hard to install.

B. Unguided (wireless) media

• Radio waves: omnidirectional, used for radio, Wi-Fi and Bluetooth.
• Microwaves: line-of-sight, directional, used for mobile networks and long-distance links with towers.
• Satellite: signals relayed through satellites for wide-area communication (TV, GPS, VSAT).
• Infrared: short range, line of sight; used in remote controls.

Why different types of networks are used: Networks differ in the area they cover, speed, cost, security and the number of users. A small office needs a fast, cheap network, while a nation or the world needs long-distance links. Hence we have:

• PAN (personal area network): within a few metres, e.g. mobile with Bluetooth.
• LAN (local area network): a building or campus; high speed, low cost.
• MAN (metropolitan area network): a city; connects several LANs.
• WAN (wide area network): a country or the world, using leased lines and satellites; the Internet is the largest WAN.

Different types are used so that each organisation can share resources (printer, files, internet), communicate, and control cost and security according to its requirements.

Intranet: A private network inside an organisation that uses Internet technologies (TCP/IP, web browsers, web servers) for sharing information.

• Access is limited to authorised members (employees), protected by a firewall.
• Used for internal email, notices, document sharing, payroll, and databases.
• It is secure, cheap and easy to manage, e.g. a bank's internal portal.

Internet: A worldwide public network of interconnected networks that uses the TCP/IP protocol to exchange data.

• Open to anyone with a connection through an ISP.
• Services: WWW, email, file transfer (FTP), social media, e-commerce, e-learning, online banking, video calls.
• Less secure and not owned by any single organisation.

An operating system (OS) is system software that manages the hardware and software resources and provides services for application programs and users. Its main functions are:

1. Process management: Creates, schedules and terminates processes; allocates the CPU fairly (multitasking), handles synchronisation and deadlocks.
2. Memory management: Keeps track of which memory is free or used, allocates memory to programs and frees it afterwards; handles virtual memory, paging and swapping.
3. File management: Creates, stores, organises, retrieves, copies, renames and deletes files and directories; controls file access permissions.
4. Device (I/O) management: Controls input/output devices through device drivers; uses buffering, caching and spooling.
5. Storage management: Allocates disk space and manages secondary storage.
6. Security and protection: Prevents unauthorised access through passwords, user accounts, permissions and encryption.
7. User interface: Provides a command-line interface (CLI) or graphical user interface (GUI) for interacting with the computer.
8. Error detection and handling: Detects hardware and software errors and takes appropriate action.
9. Resource allocation and job accounting: Allocates resources to users and keeps usage statistics.
10. Networking and communication: Allows resource sharing and communication between computers.
11. Booting and system startup: Loads the OS into memory when the computer starts.

IoT devices: The Internet of Things (IoT) is a network of physical objects embedded with sensors, software and connectivity that collect and exchange data over the internet without human intervention. Examples: smart watches, smart TVs, smart bulbs and thermostats, CCTV cameras, connected cars, smart refrigerators, wearable health trackers and industrial sensors.

Cybersecurity: Cybersecurity is the practice of protecting computers, networks, programs and data from unauthorised access, attack, damage or theft.

Features (goals) of cybersecurity:

• Confidentiality: only authorised persons can access data (encryption, passwords).
• Integrity: data stays accurate and unaltered (hashing, checksums).
• Availability: systems and data are accessible when needed (backups, redundancy).
• Authentication and authorisation: verifying identity and permissions (2-factor, biometrics).
• Non-repudiation: senders cannot deny their actions (digital signatures).
• Prevention and monitoring: firewalls, antivirus, intrusion detection and security updates.

Challenges:

• Increasing sophisticated attacks: malware, ransomware, phishing, DDoS, social engineering.
• Weak or reused passwords and human error.
• Insecure IoT devices with default passwords and no updates.
• Shortage of skilled professionals and high security costs.
• Rapidly changing technologies (cloud, mobile, AI-based attacks), insider threats.
• Data privacy laws and difficulty of tracing attackers across borders.
• Outdated software and unpatched vulnerabilities.

An expert system is an artificial intelligence program that imitates the decision-making ability of a human expert in a particular field. It stores expert knowledge and uses reasoning to solve problems and give advice.

Components:

• Knowledge base: facts and rules (IF-THEN) collected from experts.
• Inference engine: applies logic to the knowledge base to reach conclusions.
• User interface: lets the user ask questions and receive answers.
• Explanation facility: explains how a conclusion was reached.
• Knowledge acquisition module: used to add or update knowledge.

Examples: MYCIN (medical diagnosis), DENDRAL (chemistry), XCON (computer configuration).

Advantages: available 24 hours, consistent, fast, saves the cost of experts, preserves knowledge. Limitations: lacks common sense and creativity, costly to develop, works only in a narrow domain.

Applications: medical diagnosis, fault finding, financial planning, agriculture, and legal advice.

Operating systems are classified according to how they handle users and tasks:

1. Batch OS: Similar jobs are grouped into batches and executed one after another without user interaction. Used for payroll and billing. (Early IBM mainframes)
2. Multiprogramming OS: Several programs are kept in memory, and the CPU switches to another when one waits for I/O, increasing CPU use.
3. Time-sharing (multitasking) OS: The CPU time is divided into small slices among many users or tasks, giving the appearance of simultaneous execution. (Unix, Windows)
4. Multiuser OS: Allows many users to use the system at the same time from different terminals. (Linux, Unix)
5. Real-time OS (RTOS): Responds to inputs within a strict time limit. Hard real time (missile control, pacemaker) and soft real time (multimedia).
6. Distributed OS: Manages a group of independent computers and makes them look like a single system.
7. Network OS: Runs on a server to give file, printer and user sharing in a network. (Windows Server, Novell NetWare)
8. Single-user OS: One user at a time (MS-DOS); may be single-task or multitasking (Windows 10).
9. Mobile OS: Designed for smartphones and tablets (Android, iOS).
10. Embedded OS: Built into devices like ATMs, washing machines.

Ergonomics is the science of designing equipment to fit the human body so that it gives comfort, efficiency and safety, and reduces fatigue and injuries such as repetitive strain injury (RSI), carpal tunnel syndrome and back and eye strain.

Ergonomically designed devices:

• Ergonomic keyboard: split or curved layout, wrist rest; keeps hands and wrists in a natural position.
• Ergonomic mouse: vertical or contoured shape that supports the hand and reduces wrist twisting; trackballs.
• Monitor: adjustable height and tilt, anti-glare screen, blue-light filter for reduced eye strain.
• Ergonomic chair: lumbar support, adjustable height and armrests for good posture.
• Adjustable desk and footrest, laptop stand.
• Wrist rests and document holders.

Guidelines: the monitor at eye level about an arm's length away, elbows at 90 degrees, feet flat on the floor, and regular breaks (the 20-20-20 rule).

Computer: A computer is an electronic device that accepts data and instructions as input, processes them according to a stored program, stores the results, and gives output. It works fast and accurately.

Types of computers on the basis of size and speed:

1. Supercomputer: The fastest, largest and most powerful computers, with thousands of processors working in parallel (speed in petaflops). Very costly. Used for weather forecasting, nuclear research, space research, and genome analysis. Examples: Fugaku, Summit, Cray.
2. Mainframe computer: Large, powerful computers supporting hundreds or thousands of users at the same time through terminals. Used by banks, airlines, insurance and government for bulk transactions. Example: IBM z series.
3. Minicomputer (mid-range): Medium-sized, multiuser machines smaller than mainframes, used in small companies, laboratories, and manufacturing control. Examples: PDP-11, VAX, IBM AS/400.
4. Microcomputer (personal computer): Small, single-user computers built around a microprocessor. Includes desktop, laptop, notebook, tablet, smartphone, and palmtop. Used at home, office, school.
5. Embedded/workstation: Workstations are high-end single-user PCs for graphics and engineering work.

Order by size and speed: Supercomputer > Mainframe > Minicomputer > Microcomputer.

A computer system has the following main functional units:

1. Input unit: Accepts data and instructions from the user and converts them to binary. Examples: keyboard, mouse, scanner.
2. Central Processing Unit (CPU): The brain, which processes the data. It has:
   • Arithmetic Logic Unit (ALU): does arithmetic and logical operations.
   • Control Unit (CU): fetches, decodes, and directs the execution of instructions and controls all units.
   • Registers: high-speed temporary storage in the CPU.
3. Memory (storage) unit: Stores data, instructions and results. Primary memory (RAM, ROM) is used directly by the CPU; secondary memory (hard disk, SSD) stores data permanently.
4. Output unit: Presents the processed results in a human-readable form. Examples: monitor, printer, speaker.

Block diagram:

            +---------------- CPU ----------------+
 Input  --> |  Control Unit  <-->  ALU            | --> Output
 unit       |        ^  Registers  ^              |     unit
            +--------|-------------|--------------+
                     v             v
              Primary memory <--> Secondary memory

Data flows from the input unit to memory, the CPU processes it (the control unit directing the ALU), and the results are stored in memory and sent to the output unit.

Vision-based input devices: These devices capture visual information (images, video, or patterns) and convert it into digital data.

• Scanner: converts printed documents and photos into digital images.
• Digital camera / webcam: captures photos and video; used for video calls and surveillance.
• Optical Character Recognition (OCR): reads printed text and converts it to editable text.
• Optical Mark Reader (OMR): reads marks (exam answer sheets).
• Barcode and QR code reader: reads codes in shops and tickets.
• Biometric devices: fingerprint, iris and face recognition for security.
• Light pen and gesture sensors (e.g. Kinect).

Speech recognition devices: These convert spoken words into text or commands.

• Microphone with speech recognition software: the voice is captured, digitised, and matched with phonemes and language models to produce text.
• Voice assistants: Siri, Google Assistant, Alexa, which perform commands by voice.
• Dictation software: Dragon NaturallySpeaking, Google voice typing.
• Applications: voice typing, voice dialling, call centres (IVR), help for disabled persons, smart home control, and speaker identification for security.

Computer software: Software is a set of instructions (programs) and data that tells the hardware what to do. It is of two main kinds: system software and application software.

Types of application software: Application software is designed to perform specific tasks for users.

1. General-purpose (packaged) software: Ready-made software used for common tasks by many users.
   • Word processors: MS Word, Google Docs.
   • Spreadsheets: MS Excel.
   • Presentation software: PowerPoint.
   • Database software: MS Access, MySQL.
   • Web browsers, email clients, media players.
   • Graphics/DTP: Photoshop, CorelDRAW, PageMaker.
2. Customised (tailor-made) software: Developed for the specific needs of one organisation, e.g. a banking system, hospital management or payroll software for a company.
3. Integrated software / software suite: A bundle of applications that work together, e.g. MS Office, LibreOffice.
4. Utility software (application-level): Antivirus, backup, compression tools.
5. Open-source, freeware, shareware and proprietary: Classified by licensing, e.g. LibreOffice (open source), WinZip (shareware).
6. Web and mobile applications: Gmail, Facebook, WhatsApp, online banking apps.
7. Entertainment and educational software: games, e-learning, simulation, and multimedia software.

Operating system (OS): An operating system is system software that manages the computer hardware and software resources and acts as an interface between the user and the hardware. It provides services like process, memory, file and device management. Examples: Windows, Linux, macOS, Android.

Booting: Booting is the process of starting a computer and loading the operating system from secondary storage into main memory. A small program stored in ROM (BIOS) performs the Power-On Self Test (POST), then finds and loads the OS.

Cold booting: Starting the computer from the completely switched-off state by pressing the power button.

• Power is supplied to all components; the full POST is performed and the OS is loaded.
• Takes more time; also used after a power failure.
• RAM and registers are cleared.

Warm booting: Restarting a computer that is already on without switching off the power, usually when the system hangs or after installing software/updates.

• Done by Ctrl + Alt + Del, the Restart option, or the reset button.
• Faster, since some hardware tests are skipped; memory is reset but power remains on.
• Safer for the hardware than repeated power cycling.

(i) CHKDSK: Checks a disk for errors (such as lost clusters and cross-linked files), displays a status report of the disk and memory, and can repair errors.

• Syntax: CHKDSK [drive:] [/F] [/R]
• Example: CHKDSK C: /F (checks drive C and fixes errors).

(ii) TREE: Displays the directory (folder) structure of a drive or path graphically as a tree.

• Syntax: TREE [drive:][path] [/F] [/A]
• /F also displays the files in each folder. Example: TREE D:\ /F.

(iii) ATTRIB: Displays, sets or removes file attributes: read-only (R), archive (A), system (S) and hidden (H).

• Syntax: ATTRIB [+R | -R] [+A | -A] [+S | -S] [+H | -H] [drive:][path]filename
• Example: ATTRIB +H +R secret.txt hides the file and makes it read-only; ATTRIB -H secret.txt unhides it.

(iv) REN (RENAME): Changes the name of a file or directory.

• Syntax: REN [drive:][path]oldname newname
• Example: REN report.txt final.txt.

Motherboard: The motherboard (main board or system board) is the main printed circuit board of a computer, to which all components (CPU, memory, storage, expansion cards, and peripherals) are connected and through which they communicate.

Major parts:

1. CPU socket: holds the processor (e.g. LGA, PGA type) with a heat sink and fan.
2. Chipset (Northbridge and Southbridge): controls data flow between the CPU, memory, and I/O devices.
3. RAM slots (DIMM): for installing memory modules.
4. Expansion slots: PCI, PCI Express (PCIe) and AGP for graphics, sound and network cards.
5. BIOS/UEFI ROM chip and CMOS battery: stores startup instructions and keeps date/time and settings.
6. Storage connectors: SATA and M.2 ports for hard disk, SSD, and optical drives (older IDE).
7. Power connector: takes power from the power supply unit (24-pin ATX, 4/8-pin CPU).
8. I/O ports (back panel): USB, HDMI, VGA, audio, LAN, PS/2.
9. Buses: copper tracks carrying data, address and control signals.
10. Jumpers, front-panel connectors and capacitors/voltage regulators.

Secondary memory: Secondary memory (auxiliary or backing storage) is non-volatile, large-capacity storage that holds programs and data permanently. It is not directly accessed by the CPU, is slower and cheaper than primary memory, and the data is first loaded into RAM for processing.

Types:

1. Magnetic storage: data is stored as magnetised areas.
   • Hard disk drive: platters and read/write heads, capacity up to many TB.
   • Magnetic tape: sequential access, used for backup and archiving.
   • Floppy disk: now obsolete (1.44 MB).
2. Optical storage: data read and written with a laser beam.
   • CD (about 700 MB), DVD (4.7 GB or more), Blu-ray (25 GB or more).
3. Solid-state/flash storage: electronic, no moving parts.
   • SSD, pen drive (USB flash), memory cards (SD).
4. Cloud storage: data kept on internet servers (Google Drive, Dropbox).

Features: non-volatile, large capacity, cheap, often portable, slower than primary memory.

Backup: A backup is a copy of data, files and system settings made on another storage device or location so that they can be restored if the original is lost or damaged.

Importance:

• Protects against data loss caused by hardware failure, accidental deletion, virus/ransomware, theft, fire, or natural disaster.
• Allows quick recovery and business continuity.
• Gives access to older versions of files.
• Helps in migrating data to a new system and meeting legal record-keeping requirements.
• Saves time and money compared to recreating lost data.

Types of backup:

1. Full backup: copies all selected data every time. Simple and quick to restore, but needs more time and space.
2. Incremental backup: copies only the data changed since the last backup (of any type). Fast and small, but restoration needs the full backup plus all incrementals.
3. Differential backup: copies data changed since the last full backup. Restoration needs only the full and the latest differential.
4. Mirror backup: an exact real-time copy of the source.
5. Cloud / offsite backup: stored on remote servers or at another location for disaster protection.

Backups should be taken regularly, stored in a separate location, and tested.

Computer virus: A computer virus is a malicious program that attaches itself to other files or programs, replicates itself and spreads from one computer to another, causing damage to data, software, or system performance. It spreads through infected pen drives, email attachments, downloads and networks.

Symptoms that a system is infected:

• The computer becomes unusually slow, or hangs and crashes frequently.
• Programs take a long time to open, or fail to run.
• Unexpected pop-ups, advertisements or error messages appear.
• Files or folders go missing, become corrupted, or are renamed; file size changes.
• The hard disk runs out of space unexpectedly and the disk light is constantly active.
• The system restarts or shuts down by itself.
• Antivirus or firewall is disabled and cannot be started.
• The browser home page changes or unknown toolbars appear.
• Unknown programs run, strange files or icons appear on the desktop.
• High network or internet usage; emails sent to contacts without the user's knowledge.
• Weird sounds, messages or display changes.

Action: disconnect from the network, run a full antivirus scan, update the OS and antivirus, restore from backup if required.

Computer network: A computer network is a collection of two or more computers and devices connected through communication media so that they can share data, hardware (printers), software and internet connections.

Types of networks (on the basis of geographical area):

1. PAN (Personal Area Network): Covers a few metres around one person; connects devices such as phones, laptops and headphones via Bluetooth or USB.
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, low cost, and is privately owned. Uses Ethernet or Wi-Fi.
3. MAN (Metropolitan Area Network): Covers a city or a large campus (up to about 50 km). It connects several LANs, e.g. cable TV network, a bank's branches in a city.
4. WAN (Wide Area Network): Covers a country, continent or the world using telephone lines, satellites, and fibre. It has lower speed and higher cost; the Internet is the largest WAN.

Other classifications:

• By architecture: peer-to-peer (all computers are equal) and client-server (a central server provides services).
• By topology: bus, star, ring, mesh, tree.

RAID (Redundant Array of Independent/Inexpensive Disks): RAID is a technology that combines multiple physical hard disks into a single logical unit to improve performance, fault tolerance (data safety), or both.

Main levels:

• RAID 0 (striping): data split across disks; fast but no redundancy.
• RAID 1 (mirroring): identical copy on two disks; high reliability, 50% usable capacity.
• RAID 5: striping with distributed parity; needs at least 3 disks and survives one disk failure.
• RAID 6: double parity; survives two disk failures.
• RAID 10: mirroring plus striping; fast and reliable.

Difference between system bus and address bus:

A search engine is a web-based software system that searches the World Wide Web for information according to keywords entered by the user, and displays a ranked list of results (web pages, images, videos, news).

Working:

1. Crawling: programs called spiders or bots follow links and visit web pages.
2. Indexing: the content of the pages is analysed and stored in a large database (index).
3. Ranking and retrieval: when a query is entered, an algorithm ranks the matching pages by relevance and shows the results.

Examples: Google, Bing, Yahoo, DuckDuckGo, Baidu.

Uses: finding information, research, shopping, news, education and navigation. They also earn money through advertisements.

A hybrid computer combines the features of analog and digital computers. The analog part measures continuous physical quantities (temperature, pressure, speed), and the digital part does the counting, logic and storage, with converters (ADC and DAC) in between.

Features: high speed like analog, accuracy and storage like digital; used for special purposes; costly.

Examples and uses:

• Hospital ICU equipment: ECG, dialysis machines, patient monitors.
• Petrol pump (flow measurement and price display).
• Weather forecasting, scientific research, industrial process control, and defence/missile control.

Advantages: fast and accurate for special tasks, processes both kinds of data. Disadvantages: expensive, complex, not for general use.

The power supply unit (PSU) is the hardware that supplies electric power to all internal components of a computer. It converts high-voltage alternating current (AC, 110/220 V) from the mains into low-voltage direct current (DC) of +3.3 V, +5 V and +12 V required by the motherboard, drives, fans, and cards.

Main features:

• Rated in watts (e.g. 450 W, 650 W); the rating must match the system's needs.
• Contains a transformer, rectifier, filter, and voltage regulator; a fan cools it.
• Common type is SMPS (Switched Mode Power Supply), which is small, light and efficient.
• Connectors: 24-pin ATX to motherboard, 4/8-pin CPU power, SATA and Molex for drives, PCIe for graphics cards.
• Protections: over-voltage, short-circuit and overload.

A UPS or voltage stabiliser is used with the PSU to protect it against power fluctuation.

Generation of computer: A generation refers to a stage in the development of computers marked by a major change in the technology (hardware) used. It is divided into five: first (vacuum tubes, 1940-56), second (transistors, 1956-63), third (integrated circuits, 1964-71), fourth (microprocessors, 1971-present) and fifth (artificial intelligence, ULSI, present and beyond). Each generation became smaller, faster, cheaper, and more reliable.

Types of computer on the basis of working principle:

1. Analog computer: Works on continuous physical quantities such as voltage, temperature, pressure and speed. Output is shown on dials or graphs. Less accurate. Examples: speedometer, thermometer, seismograph.
2. Digital computer: Works on discrete data in binary (0 and 1) form. Fast, accurate, and general purpose, with large storage. Examples: desktop, laptop, smartphone.
3. Hybrid computer: Combines analog and digital features; the analog part measures, and the digital part processes. Examples: ECG machine in hospitals, petrol pump, industrial control systems.

The functional organisation of a computer shows its main units and how data and control signals flow between them.

                  +------------------------------+
  INPUT UNIT ---> |  CPU                         | ---> OUTPUT UNIT
 (keyboard,mouse) |  +--------+    +-----------+ |   (monitor, printer)
                  |  | Control|<-->|    ALU    | |
                  |  |  Unit  |    +-----------+ |
                  |  +---+----+     Registers    |
                  +------|-----------------------+
                         v
                +---------------------+
                |   PRIMARY MEMORY    | <---> SECONDARY MEMORY
                |   (RAM, ROM, cache) |       (HDD, SSD, DVD)
                +---------------------+

Units:

1. Input unit: takes data and instructions from the user, converts them to binary and sends them to memory/CPU.
2. Memory unit: primary memory holds the data and instructions being processed and the intermediate results; secondary memory holds data permanently.
3. CPU:
   • Control Unit (CU) fetches instructions from memory, decodes them and controls the operation of all other units.
   • Arithmetic Logic Unit (ALU) performs arithmetic and logical operations.
   • Registers hold the instruction and data being processed.
4. Output unit: converts the binary result into a human-readable form and sends it to output devices.

Working cycle: the CPU repeatedly fetches an instruction, decodes it, executes it and stores the result. Control signals come from the CU, and data moves on the buses.

Software: Software is a collection of programs, data and documentation that tells the computer hardware how to perform tasks. It is intangible.

Program: A program is a finite, ordered set of instructions written in a programming language to perform a specific task. A program is one unit of software; software consists of one or many programs.

Types of software:

1. System software: Controls and manages the hardware and gives a platform for other software.
   • Operating system: Windows, Linux, Android.
   • Language translators: compiler, interpreter, assembler.
   • Utility programs: antivirus, disk defragmenter, backup.
   • Device drivers and firmware.
2. Application software: Performs specific user tasks.
   • General purpose: word processors, spreadsheets, browsers (MS Word, Excel, Chrome).
   • Specific purpose / customised: payroll, banking, hospital management and inventory software.
3. Programming software: Tools to write programs (editors, compilers, debuggers, IDEs such as Visual Studio).

By licence: proprietary, open-source (Linux), freeware, shareware.

Peripheral devices: Peripheral devices are external hardware devices connected to a computer to give it input, display output, or store data. They are not part of the core CPU and memory. They include input devices (keyboard), output devices (printer) and storage devices (external disk).

Four input devices:

1. Keyboard: The most common input device with keys for letters, digits, symbols, function and control keys (QWERTY layout). Pressing a key generates a code that is sent to the computer. Used for typing text and commands.
2. Mouse: A pointing device that moves a cursor on the screen and has buttons (left, right) and a scroll wheel. Types: mechanical, optical, wireless. Used for selecting, clicking and dragging in a GUI.
3. Scanner: An optical input device that converts printed documents, photos and drawings to digital images. Types: flatbed, handheld, sheet-fed. With OCR it converts printed text to editable text.
4. Microphone: Converts sound waves into electrical signals which the sound card digitises. Used for recording, voice calls, and speech recognition.

Other input devices: webcam, touch screen, joystick, barcode reader.

SSD (Solid State Drive): An SSD is a storage device that stores data on interconnected flash memory chips (NAND), with no moving parts. It is used instead of a hard disk drive in computers.

Why SSDs are more popular than HDDs:

Because of the speed, reliability, silent operation, low power use and a fall in prices, SSDs are now widely used in laptops, mobiles and even servers. HDDs remain only for cheap bulk storage and backups.

Cache memory: Cache memory is a very fast, small, expensive memory (made of SRAM) placed between the CPU and main memory (RAM) that stores frequently used data and instructions. The CPU checks the cache first; a hit gives the data quickly, while a miss means data is fetched from RAM. This reduces the average access time and speeds up processing.

• L1 cache: inside the CPU core; smallest (KBs) and fastest.
• L2 cache: larger (hundreds of KB to MB), slightly slower; per core or shared.
• L3 cache: shared by all cores; several MB.

Types of computer memory:

1. Primary memory: directly accessed by the CPU.
   • RAM: volatile read/write memory; SRAM (fast, used as cache) and DRAM (main memory).
   • ROM: non-volatile; PROM, EPROM, EEPROM; stores BIOS.
   • Cache memory and registers.
2. Secondary memory: non-volatile, large and slower; magnetic (hard disk, tape), optical (CD, DVD, Blu-ray) and flash (SSD, pen drive).
3. Virtual memory: part of the hard disk used as an extension of RAM.

Hierarchy (fast to slow): Registers > Cache > RAM > Secondary storage. Speed and cost per bit fall, while capacity rises, as we go down.

Broadband is a high-capacity, always-on internet connection that carries many signals (data, voice, video) at the same time over a single medium, at speeds much higher than traditional dial-up. It is delivered through technologies such as optical fibre (FTTH), DSL/ADSL, cable modem, fixed wireless and satellite. Its key features are high bandwidth, constant connectivity, and the ability to use voice and data simultaneously.

Difference between LAN, WAN and MAN

Operating System (OS) is system software that manages the hardware and software resources of a computer and provides a convenient interface between the user and the hardware. It handles processes, memory, files, devices and security. Examples: Windows, Linux, macOS, Android.

Types of operating system

1. Batch OS: Similar jobs are collected into batches and executed one after another without user interaction. It gives good throughput but has long turnaround time and no interaction. Example: early IBM mainframe systems, payroll processing.
2. Multiprogramming OS: Several programs are kept in memory and the CPU switches to another when one waits for I/O, so CPU utilisation is high.
3. Time-sharing (multitasking) OS: The CPU time is divided into small slices given to each user or task in turn, giving the illusion of simultaneous execution and quick response. Example: UNIX, Linux, Windows.
4. Multiuser OS: Allows many users to use the system at the same time through terminals. Example: UNIX, Linux server.
5. Multiprocessing OS: Uses two or more CPUs in one computer that share memory and work in parallel, improving speed and reliability.
6. Real-time OS (RTOS): Gives a guaranteed response within a fixed deadline. Hard real-time (missile control, pacemaker) and soft real-time (multimedia streaming). Example: VxWorks, QNX.
7. Distributed OS: Manages a group of independent computers connected by a network so they appear as one system, sharing resources and load. Example: LOCUS, Amoeba.
8. Network OS: Runs on a server and provides file, printer and user management to client computers. Example: Windows Server, Novell NetWare.
9. Embedded / Mobile OS: Small OS in devices such as phones, routers and appliances. Example: Android, iOS, FreeRTOS.
10. Single-user OS: Supports one user at a time (MS-DOS single task, Windows 98) and GUI vs CUI based interfaces are another classification.

Machine Learning (ML) is a branch of Artificial Intelligence in which a computer learns patterns from data and improves its performance on a task through experience, without being explicitly programmed with rules for every case.

Types of machine learning

1. Supervised learning: The model is trained on labelled data (input with the correct output). It learns a mapping from input to output and predicts labels for new data.
   • Types: classification (discrete output) and regression (continuous output).
   • Examples: spam detection in email, house price prediction, disease diagnosis. Algorithms: linear regression, decision tree, SVM, k-NN.
2. Unsupervised learning: The data has no labels. The model finds hidden structure or groups by itself.
   • Types: clustering, association, dimensionality reduction.
   • Examples: customer segmentation, market basket analysis ("people who buy bread also buy butter"). Algorithms: k-means, PCA, Apriori.
3. Semi-supervised learning: Uses a small amount of labelled data with a large amount of unlabelled data. Example: classifying web pages or photos when only a few are labelled.
4. Reinforcement learning: An agent interacts with an environment, takes actions and receives rewards or penalties, learning a policy that maximises total reward. Examples: game-playing programs (chess, Go), robot navigation, self-driving cars. Algorithms: Q-learning.

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, perception, understanding language and decision making.

Applications of AI

• Healthcare: disease diagnosis from X-ray/MRI images, drug discovery, patient monitoring, robotic surgery.
• Education: personalised learning, intelligent tutoring systems, automatic grading, chatbots.
• Banking and finance: fraud detection, credit scoring, algorithmic trading, customer-service chatbots.
• Agriculture: crop disease detection, yield prediction, smart irrigation, drones for monitoring.
• Transport: self-driving cars, traffic prediction, route optimisation (Google Maps).
• Natural language and speech: virtual assistants (Siri, Alexa, Google Assistant), machine translation, speech-to-text.
• E-commerce and entertainment: recommendation systems (Amazon, Netflix, YouTube), targeted advertising.
• Robotics and industry: industrial robots, predictive maintenance, quality inspection.
• Security: face recognition, intrusion detection, spam and malware filtering.
• Games: AI opponents in chess, Go and video games.

Electronic card-based devices store or process data on a plastic card and are used for identification, payment and access in the digital world.

1. Magnetic stripe card: Data is stored on a magnetic stripe at the back and read by swiping through a reader. Easy to copy, so less secure. Example: older ATM/debit and credit cards, hotel key cards.
2. Smart card (chip card): Contains an embedded microprocessor and memory that can store and process data securely. Types are contact (EMV chip cards) and contactless (NFC). Example: chip debit/credit card, SIM card, national ID, e-passport.
3. RFID / proximity card: A tag with an antenna and chip that communicates by radio waves at short distance, without contact. Example: office access cards, library cards, toll and metro cards.
4. Contactless (NFC) payment card: Payment is made by tapping near a terminal. Example: tap-to-pay cards and mobile wallets.
5. ATM / debit card: Linked to a bank account for cash withdrawal and payments using a PIN.
6. Credit card: Allows purchase on credit up to a limit, to be repaid later.
7. Prepaid / stored-value card: Holds a preloaded balance. Example: mobile recharge cards, transport cards, gift cards.
8. Memory card: Flash storage card used in cameras and phones. Example: SD, microSD.
9. Identity / biometric card: Stores a person's identity and fingerprint/photo. Example: National ID card, driving licence.

These cards make transactions faster and safer, reduce cash handling, and allow access control and identification.

Booting is the process of starting a computer and loading the operating system into main memory (RAM) so that it is ready for use. The term comes from "bootstrapping".

Steps of booting:

1. Power is switched on and the CPU starts executing the BIOS/UEFI firmware stored in ROM.
2. POST (Power-On Self Test) checks the CPU, RAM, keyboard, disk and other hardware.
3. The BIOS finds the boot device using the boot order and reads the boot sector / MBR.
4. The bootstrap loader loads the OS kernel into RAM.
5. The OS initialises drivers and services and shows the desktop or login screen.

Types of booting:

• Cold boot (hard boot): starting the computer from the power-off state.
• Warm boot (soft boot): restarting a running computer using Ctrl+Alt+Del or the Restart option, without turning off the power; POST is usually skipped.

Computer is an electronic device that accepts data as input, processes it under the control of stored instructions (a program), stores it, and produces useful information as output, quickly and accurately.

Application areas of computer

1. Education: e-learning, online classes, digital libraries, result processing, simulations and research.
2. Business and office: accounting, payroll, inventory, word processing, spreadsheets, e-commerce and email.
3. Banking and finance: ATMs, core banking, mobile banking, online payment, stock trading.
4. Healthcare: patient records, diagnosis equipment (CT, MRI, ECG), telemedicine, hospital management.
5. Communication: email, social media, video conferencing, VoIP and messaging.
6. Government: e-governance, tax filing, citizen databases, voting and census.
7. Science and engineering: CAD/CAM, design and simulation, weather forecasting, space research.
8. Entertainment: games, movies, music, animation and graphics.
9. Transport and tourism: ticket reservation, air traffic control, GPS navigation.
10. Industry and manufacturing: robotics, process control, automation.
11. Defence and security: surveillance, missile guidance, cyber security.
12. Agriculture and home: crop information, smart devices, home budgeting.

A digital computer works on discrete (binary) data and consists of the following units.

        +-----------------------------------------+
        |              CPU                        |
        |   +-----------+        +-------------+  |
Input ->|   |  Control  |<------>|    ALU      |  |-> Output
Unit    |   |   Unit    |        +-------------+  |   Unit
        |   +-----------+                          |
        +----------------^------------------------+
                         |
                  +--------------+      +------------+
                  | Main memory  |<---->| Secondary  |
                  +--------------+      |  storage   |
                                        +------------+

1. Input unit: Accepts data and instructions from the user and converts them into binary form for the computer. Examples: keyboard, mouse, scanner, microphone.
2. Central Processing Unit (CPU): The brain of the computer, made of:
   • Arithmetic Logic Unit (ALU): performs arithmetic (add, subtract, multiply, divide) and logical (AND, OR, NOT, comparisons) operations.
   • Control Unit (CU): fetches, decodes and directs execution of instructions and coordinates all units by control signals.
   • Registers: small, very fast storage inside the CPU (accumulator, program counter, instruction register).
3. Memory unit: Stores data and instructions. Primary memory (RAM, ROM, cache) is directly accessed by the CPU; secondary memory (HDD, SSD, optical disk) stores data permanently and in bulk.
4. Output unit: Converts the processed binary results into human-readable form. Examples: monitor, printer, speaker, plotter.

Software is a set of programs, data and instructions that tells the hardware what to do and how to do it. It is intangible and is classified mainly as system software, application software and programming software.

Types of software

1. System software: Controls and manages hardware and provides a platform to run other software.
   • Operating system: Windows, Linux, Android.
   • Utility programs: antivirus, disk cleanup, backup, file compression.
   • Device drivers: let the OS communicate with hardware such as a printer.
   • Language translators: compiler, interpreter, assembler.
   • Firmware/BIOS.
2. Application software: Programs designed for a specific user task.
   • General-purpose: MS Word, Excel, PowerPoint, browsers.
   • Specific-purpose: payroll, hotel management, airline reservation, accounting software.
   • Custom (tailor-made) and packaged software.
3. Programming software: Tools that programmers use to write and test programs, such as editors, compilers, debuggers and IDEs (Visual Studio, Eclipse).

By licence: proprietary, freeware, shareware, open-source (Linux, Firefox).

A Solid State Drive (SSD) stores data in NAND flash memory chips with no moving parts, whereas a hard disk drive (HDD) uses spinning magnetic platters and a moving read/write head. This makes the SSD more efficient in the following ways.

1. Speed: SSDs read/write at about 500 MB/s (SATA) to several GB/s (NVMe), while an HDD gives about 80 to 160 MB/s. Boot time and application loading are much shorter.
2. Access time: SSD access time is about 0.1 ms, since there is no seek time or rotational latency; an HDD takes about 5 to 10 ms.
3. Durability: No moving parts means resistance to shock and vibration, so data is less likely to be lost if a laptop is dropped.
4. Power consumption and heat: SSDs use less power and give out less heat, extending battery life.
5. Noise: Silent, whereas HDDs make spinning and clicking noise.
6. Size and weight: Smaller, lighter and available in compact forms (M.2), suited to thin laptops.
7. Reliability and no fragmentation penalty: Random access is equally fast, so fragmentation does not slow it down.

Limitations: higher cost per GB and limited write cycles, but these are acceptable for most users. Hence the SSD is more efficient than an HDD for performance-critical use.

Peripheral devices are external hardware devices connected to the computer to give input, receive output or store data, and they are not part of the CPU and main memory. They are classified as input devices (keyboard, mouse), output devices (monitor, printer) and storage devices (hard disk, pen drive).

Five output devices

1. Monitor: The main output device that displays text, images and video. Types: CRT, LCD, LED and OLED. Quality depends on resolution, refresh rate and size.
2. Printer: Produces hard copy on paper.
   • Impact (dot-matrix): strikes the ribbon; can make carbon copies.
   • Non-impact (inkjet, laser): sprays ink or uses toner and laser; quiet and good quality.
3. Speaker / headphones: Convert digital audio signals into sound, used for music, voice and alerts. They need a sound card.
4. Plotter: Prints large, high-precision drawings using pens or inkjet. Used for engineering drawings, maps and architectural plans (CAD).
5. Projector: Displays the computer screen on a large screen or wall for presentations and classrooms. Types: LCD, DLP.

Other output devices include the GPS display, braille displays and 3D printers.

Ergonomics is the design of equipment to fit the human body so that use is comfortable, safe and efficient. Ergonomic devices increase efficiency of users in these ways.

• Reduce fatigue and strain: An ergonomic keyboard (split, curved or with a palm rest) and a vertical or contoured mouse keep wrists and forearms in a natural position, reducing Repetitive Strain Injury (RSI) and carpal tunnel syndrome.
• Better posture: Adjustable chairs with lumbar support, monitor stands at eye level and laptop stands prevent back, neck and shoulder pain, so users can work longer in comfort.
• Less eye strain: Anti-glare, adjustable screens and proper lighting reduce headaches and tiredness.
• Faster, more accurate work: Comfortable, well-placed devices (trackball, touchpad, adjustable desks, footrest) lead to fewer errors and less time lost to discomfort.
• Fewer health problems and absence: Healthy users are more productive and take fewer sick leaves.

Thus ergonomic design raises comfort, productivity and long-term health.

Use of cache memory: Cache is a small, very fast memory (SRAM) between the CPU and RAM. It stores frequently used data and instructions so the CPU can get them quickly without waiting for slower RAM. This reduces the access time, bridges the speed gap between CPU and RAM and improves overall performance. It exists in levels: L1 (inside the core, smallest and fastest), L2 and L3 (larger, shared).

Three types of primary memory

1. RAM (Random Access Memory): Volatile read/write memory that holds the programs and data currently in use. Its contents are lost when power is off. Types: SRAM (fast, used for cache, costly) and DRAM (slower, cheaper, used as main memory). Use: working storage for the OS, applications and data being processed.
2. ROM (Read Only Memory): Non-volatile memory whose contents are written by the manufacturer and are only read. Types: PROM, EPROM, EEPROM, flash. Use: stores the BIOS/bootstrap program that starts the computer.
3. Cache memory: Described above, used to speed up access to frequently used data.

(Registers inside the CPU are also primary memory and hold the data currently being processed.)

Data communication is the exchange of data (text, audio, video) between two or more devices through a transmission medium. Its components are sender, receiver, message, medium and protocol. Its effectiveness depends on delivery, accuracy, timeliness and jitter.

Transmission media

A. Guided (wired) media

1. Twisted pair cable: Two insulated copper wires twisted together to reduce interference. UTP (used in LANs, Cat5e/Cat6, up to 100 m) and STP (shielded). Cheap and easy to install but limited distance and bandwidth.
2. Coaxial cable: A central copper conductor with insulation, a metallic shield and an outer jacket. Higher bandwidth and better noise protection than twisted pair. Used in cable TV and older Ethernet.
3. Optical fibre: Carries data as light pulses through glass or plastic cores (single-mode, multi-mode). Very high bandwidth, long distance, immune to electromagnetic interference, secure; but costly and harder to install.

B. Unguided (wireless) media

1. Radio waves: Omnidirectional, used for radio, Wi-Fi and Bluetooth.
2. Microwave: Line-of-sight, high-frequency, used for point-to-point links and mobile networks.
3. Infrared: Short-range line-of-sight, used in remote controls.
4. Satellite: Signals relayed through satellites for wide-area coverage (TV, GPS, VSAT).

Operating System (OS) is system software that acts as an interface between the user and the computer hardware and manages all resources of the computer.

Functions of an operating system

1. Process management: Creates, schedules and terminates processes; allocates the CPU using scheduling algorithms; handles synchronisation, communication and deadlock.
2. Memory management: Allocates and frees main memory, keeps track of used and free areas, and supports virtual memory, paging and segmentation.
3. File management: Creates, deletes, reads, writes, names and organises files and directories, and controls access permissions.
4. Device management: Controls input/output devices through device drivers, using buffering, caching and spooling.
5. Secondary storage management: Allocates disk space, manages free space and schedules disk access.
6. Security and protection: Protects data from unauthorised access using passwords, authentication, permissions and encryption.
7. User interface: Provides a command line (CUI) or graphical (GUI) interface.
8. Job scheduling and resource allocation: Shares resources fairly among users and tasks.
9. Error detection and handling: Detects and responds to hardware and software errors.
10. Networking and accounting: Supports communication between computers and records resource usage.

Operating system architecture (layered view)

+------------------------------------------+
|   Users / Application programs           |
+------------------------------------------+
|   User interface (Shell: GUI / CLI)      |
+------------------------------------------+
|   System calls / API                     |
+------------------------------------------+
|   Kernel: process, memory, file,         |
|   device management, security            |
+------------------------------------------+
|   Device drivers / BIOS firmware         |
+------------------------------------------+
|   Hardware: CPU, memory, I/O devices     |
+------------------------------------------+

The user and applications work through the shell, which passes requests to the kernel through system calls. The kernel manages the hardware via device drivers.

Types of operating systems

1. Batch OS: Jobs of a similar type are grouped and executed without user interaction.
2. Multiprogramming / multitasking (time-sharing) OS: Several programs share the CPU through time slices. Example: Windows, Linux.
3. Multiuser OS: Many users use the system at once. Example: UNIX.
4. Multiprocessing OS: Uses several CPUs in parallel for high speed.
5. Real-time OS: Responds within strict time limits; used in industrial control, aircraft and medical devices. Example: VxWorks.
6. Distributed OS: Many networked computers work as one system.
7. Network OS: Provides shared files, printers and users on a network. Example: Windows Server.
8. Mobile / embedded OS: Android, iOS, and the OS inside appliances.

Artificial Intelligence (AI) is the ability of a computer or machine to imitate human intelligence, performing tasks such as learning, reasoning, problem solving, understanding language and recognising images or speech.

Three applications

1. Healthcare: AI analyses medical images (X-ray, CT, MRI) to detect diseases such as cancer early, predicts patient risk, helps in drug discovery and powers robotic surgery and virtual health assistants. It improves accuracy and speed of diagnosis.
2. Natural language processing and virtual assistants: Systems like Siri, Alexa and Google Assistant, chatbots and machine translation understand speech and text, answer queries and perform tasks, such as setting alarms or translating languages.
3. Self-driving vehicles and transport: Using cameras, sensors and machine learning, autonomous cars detect roads, obstacles and signals and decide how to drive. AI is also used in traffic prediction and route planning.

Other uses include fraud detection in banking, recommendation systems and smart agriculture.

Blockchain is a distributed, decentralised digital ledger that records transactions in linked blocks across many computers (nodes) in a way that makes the records secure and very difficult to alter.

Structure: Each block contains transaction data, a timestamp, its own hash and the hash of the previous block. Because of this link, changing one block changes its hash and breaks all following blocks, so tampering is easily detected.

How it works:

1. A transaction is requested and broadcast to the network of nodes.
2. Nodes validate it using a consensus mechanism (Proof of Work, Proof of Stake).
3. Valid transactions are grouped into a new block.
4. The block is added to the chain and the ledger is updated on all nodes.

Features: decentralisation (no central authority), transparency, immutability, security through cryptography, and traceability.

Types: public (Bitcoin, Ethereum), private, consortium and hybrid.

Applications: cryptocurrency, supply chain tracking, smart contracts, digital identity, voting, land and health records.

Limitations: high energy use (PoW), scalability, and regulatory uncertainty.

Cybersecurity is the practice of protecting computers, networks, programs and data from unauthorised access, attack, damage or theft. It aims to maintain the CIA triad: Confidentiality (only authorised people can see data), Integrity (data is not altered improperly) and Availability (systems and data are accessible when needed).

Common threats: malware (virus, worm, ransomware, trojan), phishing, denial-of-service (DoS/DDoS), man-in-the-middle attacks, password attacks, SQL injection and social engineering.

Types of cybersecurity: network security, application security, information (data) security, endpoint security, cloud security and operational security.

Protective measures:

• Firewalls and antivirus/anti-malware software.
• Strong passwords and multi-factor authentication.
• Encryption of data in storage and transit.
• Regular updates and patching, and backups.
• Intrusion detection systems and user awareness training.

Importance: protects personal and financial information, prevents loss of money and reputation, and keeps essential services working.

Data transmission modes describe the direction of data flow between two connected devices.

1. Simplex: Data flows in one direction only. The sender can only send and the receiver can only receive. Example: keyboard to computer, radio and TV broadcast.
2. Half duplex: Data can flow in both directions but only one direction at a time. Example: walkie-talkie, CB radio.
3. Full duplex: Data can flow in both directions at the same time. Example: telephone, mobile phone, Ethernet.

Full duplex gives the highest efficiency but needs more bandwidth or channels.

Computer is an electronic machine that accepts data, processes it according to instructions and produces information as output, with speed and accuracy.

Generations of computers

Each generation gave smaller size, higher speed, lower cost, lower power consumption and greater reliability.

Functions performed by a computer

1. Input: accepting data and instructions.
2. Processing: performing arithmetic and logical operations on data.
3. Storage: saving data, instructions and results.
4. Output: presenting the results in usable form.
5. Control: directing and coordinating all the operations.

Functional diagram

            +-------------------- Control Unit ---------------------+
            |                          |                            |
 Input  ----> [Input unit] ---> [ Memory unit ] <---> [ ALU ] ---> [Output unit] ----> Output
 (data)                              ^                                              
                                     |                                              
                              [Secondary storage]

Functions of each unit

• Input unit: Takes data and programs from input devices (keyboard, mouse, scanner) and converts them to binary form the computer understands.
• Memory (storage) unit: Holds the data, instructions, intermediate and final results. Primary memory is fast and temporary; secondary memory is permanent.
• Arithmetic Logic Unit (ALU): Performs arithmetic operations (+, -, ×, ÷) and logical operations (AND, OR, NOT, comparison).
• Control Unit (CU): Fetches instructions from memory, decodes them, and sends control signals to the other units so that they are executed in the correct order. It does not process data itself.
• Output unit: Converts the results from binary into readable form and sends them to output devices such as monitor and printer.

ALU and CU together form the CPU.

Processor (CPU) is the main chip of a computer that fetches, decodes and executes instructions. It consists of the ALU, control unit and registers, and is the brain of the computer.

Types of processors

By instruction set architecture:

1. CISC (Complex Instruction Set Computer): Many complex instructions of variable length; one instruction may do several operations. Example: Intel x86 and AMD.
2. RISC (Reduced Instruction Set Computer): Small set of simple, fixed-length instructions executed in about one cycle; efficient and low power. Example: ARM (mobile phones), MIPS, RISC-V.

By number of cores: 3. Single-core: one processing unit. 4. Dual-core, quad-core, hexa-core, octa-core: two or more cores on one chip that run tasks in parallel (multi-core).

By purpose or word size: 5. Microprocessor: a whole CPU on one chip, 32-bit or 64-bit (Intel Core i3/i5/i7/i9, AMD Ryzen). 6. Microcontroller: CPU with memory and I/O on one chip, for embedded systems (8051, Arduino AVR). 7. Digital signal processor (DSP): specialised for audio, video and signal processing. 8. GPU: Graphics processor with many cores for graphics and AI. 9. Co-processor / SoC (System on Chip): math co-processor or a chip combining CPU, GPU and memory controller, used in smartphones (Snapdragon, Apple A-series).

Client-server model is a network architecture in which a powerful computer called the server provides services and resources (files, web pages, databases, printing) and many clients request those services over the network. The server waits for requests and responds; clients initiate them. Examples: web browser (client) and web server, email client and mail server. It gives centralised control, security and easy backup, but the server is a single point of failure and may be overloaded.

LAN topologies

1. Bus topology: All devices connect to a single backbone cable with terminators at both ends.
   • Characteristics: one common cable, data travels in both directions.
   • Advantages: cheap, easy to install, needs little cable.
   • Disadvantages: backbone failure stops the whole network, performance drops with traffic, difficult to troubleshoot.
2. Star topology: Every device connects to a central hub or switch.
   • Advantages: easy to add or remove nodes, failure of one cable affects only one node, easy fault finding.
   • Disadvantages: central device failure brings down the network, more cable and cost.
3. Ring topology: Devices form a closed loop; data passes from node to node (token passing).
   • Advantages: orderly access, no collisions, equal access.
   • Disadvantages: one break can stop the network (unless dual ring), adding nodes disturbs the network.
4. Mesh topology: Every device connects to every other (full mesh needs n(n-1)/2 links).
   • Advantages: very reliable, multiple routes, easy fault isolation, secure.
   • Disadvantages: very costly, complex wiring and configuration.
5. Tree topology: Hierarchy of star networks connected to a root bus. Scalable and easy to manage, but depends on the root and backbone.
6. Hybrid topology: A combination of two or more topologies; flexible and scalable but complex and costly.

Operating system versus other software

Major functions of OS

1. Process management: creation, scheduling and termination of processes, and CPU allocation.
2. Memory management: allocation and deallocation of RAM, virtual memory, paging.
3. File management: creating, organising, protecting and accessing files and folders.
4. Device management: controlling I/O devices through drivers, buffering and spooling.
5. Security and protection: authentication and access control.
6. User interface: command line or GUI.
7. Error handling and resource accounting: detecting errors, tracking usage of resources.
8. Networking support: communication between computers.

SMPS (Switched Mode Power Supply) is the power supply unit in a computer that converts AC mains supply (220 V in Nepal) into regulated low-voltage DC (+3.3 V, +5 V, +12 V, -12 V) required by the computer's components. It first rectifies and filters AC to DC, then a high-frequency switching transistor chops the DC, a small transformer steps it down, and it is rectified and regulated again. It is light, small, efficient (about 70 to 90 percent) and has little heat, compared with a linear power supply. It also has protection against over-voltage and short circuit.

UPS (Uninterruptible Power Supply) supplies backup power from a battery when the mains fails and also conditions the supply, protecting the computer from data loss and damage.

Types of UPS

1. Offline (standby) UPS: Normally the load is fed directly from mains; when power fails or drops, it switches to the inverter and battery in about 2 to 10 ms. Cheap and simple, but offers little protection against surges and voltage variation. Used for home PCs.
2. Line-interactive UPS: Has an automatic voltage regulator (AVR) that corrects over- and under-voltage without using the battery; switches to battery only on power failure. Better protection, medium cost, used for small offices and servers.
3. Online (double-conversion) UPS: Incoming AC is continuously converted to DC (charging the battery) and then back to clean AC by an inverter, so the load is always powered by the inverter. Zero transfer time and full protection against spikes and noise, but costly and less efficient. Used for servers and data centres.

(i) COPY CON: Creates a new text file by copying what is typed on the console (keyboard) into a file.

Syntax: COPY CON [drive:][path]filename

Example: COPY CON notes.txt, then type the text and press Ctrl+Z (or F6) and Enter to save the file.

(ii) TYPE: Displays the contents of a text file on the screen without modifying it.

Syntax: TYPE [drive:][path]filename

Example: TYPE notes.txt

(iii) SCANDISK: An external command that checks a disk for logical (file system) and physical (surface) errors, and repairs them, such as lost clusters and cross-linked files.

Syntax: SCANDISK [drive:] [/AUTOFIX] [/CHECKONLY] [/SURFACE]

Example: SCANDISK C: /AUTOFIX (in newer Windows, the equivalent is CHKDSK).

(iv) PING: Tests the connectivity between the local computer and another computer or host on a network by sending ICMP echo requests and showing the reply time and packet loss.

Syntax: PING [-t] [-n count] hostname_or_IP

Example: PING 192.168.1.1 or PING www.google.com

Virus-nature programs (malware) are malicious programs designed to damage, disrupt or steal data from a computer system. A true virus attaches itself to a host file and spreads when the file is run.

Types with examples

1. File infector (parasitic) virus: Attaches to executable files (.exe, .com) and runs when the file runs. Example: Jerusalem, Cascade.
2. Boot sector virus: Infects the boot sector or MBR of a disk and loads at start-up. Example: Michelangelo, Stoned.
3. Macro virus: Written in macro language and infects documents and spreadsheets (Word, Excel). Example: Melissa.
4. Polymorphic / metamorphic virus: Changes its code each time to avoid detection by antivirus.
5. Worm: Self-replicating program that spreads over networks without a host file, consuming bandwidth. Example: ILOVEYOU, Code Red, Blaster.
6. Trojan horse: Looks like a useful program but carries a hidden malicious function (backdoor, data theft); does not self-replicate. Example: Zeus.
7. Ransomware: Encrypts files and demands payment. Example: WannaCry.
8. Spyware and adware: Secretly collect user information or show unwanted ads.
9. Logic bomb: Triggers when a particular condition or date occurs.
10. Rootkit and botnet malware: Hide the attacker's presence and take remote control of machines.

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

Types of bus (by function)

1. Data bus: Carries data between CPU, memory and I/O devices. It is bidirectional, and its width (8, 16, 32, 64 bits) determines how much data is transferred at a time.
2. Address bus: Carries the memory or I/O address from the CPU to specify the location to read or write. It is unidirectional. An n-bit address bus can address $2^n$ locations; for example, a 32-bit bus addresses $2^{32}$ = 4 GB.
3. Control bus: Carries control and timing signals such as Read, Write, Interrupt, Clock and Reset, which coordinate the units. It is bidirectional.

Other classifications

• System bus (front side bus): connects CPU, main memory and I/O.
• Internal (local) bus: inside the CPU. External/expansion bus: connects peripheral devices; examples are PCI, PCI Express, USB, SATA, AGP.

A core is an independent processing unit inside a CPU. The development of multi-core processors (Core 2 Duo, Core i3, i5, i7, i9) has increased the processing capacity of computers in several ways.

• Parallel processing: Dual, quad, hexa and octa-core processors run several tasks or threads at the same time, so multitasking is faster and smoother.
• Better performance at lower clock speed: Instead of raising the clock frequency (which produces much heat), more cores share the workload, giving higher throughput with lower power consumption and heat.
• Hyper-threading: Each core can handle two threads, making better use of the core.
• Larger and shared cache (L1, L2, L3) and faster memory controllers reduce waiting time for data.
• Turbo boost: Increases the clock of active cores when the load is high.
• Support for 64-bit architecture and advanced instruction sets, plus integrated graphics, increasing speed for heavy applications such as video editing, games and virtual machines.

Overall, the number of tasks completed per second increases, since the workload is divided among cores.

A hard disk drive (HDD) is a magnetic secondary storage device that stores data permanently on rotating platters.

Block diagram / structure

  +-----------------------------------------------+
  |  Platters (stacked, coated with magnetic     |
  |  material) on a Spindle  -> rotate 5400-7200 |
  |  rpm                                          |
  |       ^  Read/Write heads on Actuator arm     |
  |       |  moved by Voice-coil actuator         |
  +-----------------------------------------------+
        |                       |
   Disk controller  <-->  Interface (SATA) <--> CPU/Memory

Parts: platters, spindle motor, read/write heads, actuator arm, voice-coil motor and a controller board.

Organisation of data: Each platter surface is divided into concentric tracks, each track into sectors (usually 512 bytes or 4 KB); the same track on all platters forms a cylinder; sectors are grouped into clusters.

Storage mechanism:

• Writing: The head produces a magnetic field by current in its coil, which magnetises tiny regions of the platter surface in one of two directions, representing binary 1 and 0.
• Reading: As the magnetised regions pass under the head, they induce a current (or resistance change) that is detected and converted into bits.
• The platter spins, and the actuator moves the head over the required track (seek time), then waits for the required sector to come under it (rotational latency); the data is then transferred. Access time = seek time + rotational latency + transfer time.
• The head floats on a thin air cushion above the surface, without touching it.

Capacity = surfaces × tracks per surface × sectors per track × bytes per sector.

Backup is a copy of data stored separately so that it can be restored after loss caused by hardware failure, deletion, virus attack or disaster.

Types of backup

1. Full backup: Copies all selected data every time. Simplest and fastest to restore, but takes the most time and space.
2. Incremental backup: Copies only the data changed since the last backup of any type. Fast and uses little space, but restoring needs the last full backup and all incrementals.
3. Differential backup: Copies all data changed since the last full backup. Restoring needs only the last full and last differential; it needs more space than incremental.
4. Mirror backup: An exact copy of the source, updated continuously.
5. Location-based: local (external disk, tape), offsite and cloud backup.

Cloud backup

Cloud backup (online backup) sends a copy of data over the Internet to a remote server run by a provider (Google Drive, OneDrive, Dropbox, AWS) and stores it there.

• Advantages: protects against local disasters such as fire and theft, automatic scheduled backup, access from anywhere, scalable storage, no hardware to buy, data encryption.
• Disadvantages: needs a fast Internet connection, recurring subscription cost, slow first backup and restore, dependence on provider, and privacy concerns.

Power caring factors are the measures taken to protect the computer from power problems and to give it a clean, stable supply.

Power problems: blackout (total loss), brownout/sag (low voltage), surge/spike (sudden high voltage), noise (electrical interference) and frequency variation.

Caring measures:

• Voltage stabiliser / AVR: keeps output voltage constant when mains varies.
• UPS: gives battery backup so the computer can shut down properly without data loss.
• Surge protector / spike guard: protects against sudden over-voltage and lightning.
• Proper earthing (grounding): safely removes leakage current and static charge and avoids shocks and damage.
• Isolation transformer and line conditioner: remove noise.
• Good-quality SMPS with proper rating and clean, loose-free wiring.
• Switching off and unplugging during thunderstorms, and not overloading sockets.

ATX power supply (Advanced Technology eXtended) is the standard form factor of computer power supply unit (SMPS) introduced by Intel in 1995 and used with ATX motherboards. It converts 220 V AC into regulated DC voltages.

Features:

• Outputs: +3.3 V, +5 V, +12 V, -12 V and a +5 V standby (5VSB).
• Soft power: it has a PS_ON signal from the motherboard, so the computer can be switched on and off by software (shutdown, wake on LAN), unlike older AT supplies with a mechanical switch.
• Main connector of 20 pins (later 24 pins), a 4/8-pin CPU power connector, SATA, Molex and PCIe connectors.
• Has a cooling fan, over-voltage, short-circuit and over-load protection.
• Power rating is in watts (for example 450 W, 600 W).

Advantage: better efficiency, software-controlled power management and improved airflow.

LCD (Liquid Crystal Display) is a flat-panel display technology that uses liquid crystals to produce images. The liquid crystals do not emit light themselves; they control the passage of light from a backlight (CCFL or LED).

Working: A layer of liquid crystal is between two polarising filters and glass plates with electrodes. When voltage is applied, the crystals twist or untwist, controlling how much light from the backlight passes through; colour filters (red, green, blue) form coloured pixels.

Types: TN, IPS and VA panels; passive-matrix and active-matrix (TFT) LCD.

Advantages: thin and light, low power consumption, no flicker, sharp image, little radiation.

Disadvantages: limited viewing angle in some types, lower contrast and black levels than OLED, backlight needed, and response time can be slower.

Uses: monitors, laptops, TVs, mobile phones, calculators and watches.