Computer Basics & Generations
What is a Computer?
An electronic device that processes data according to instructions (programs). Full cycle: Input → Process → Output → Storage
IPO Cycle: Input (keyboard, mouse) → Processing (CPU) → Output (monitor, printer) → Storage (HDD, RAM)
Generations of Computers
| Generation | Period | Technology | Examples | Characteristics |
|---|---|---|---|---|
| 1st | 1940–56 | Vacuum Tubes | ENIAC, UNIVAC | Huge size, high power, low speed, machine language |
| 2nd | 1956–63 | Transistors | IBM 1401 | Smaller, faster, less heat, assembly language |
| 3rd | 1964–71 | Integrated Circuits (IC) | IBM 360 series | Even smaller, high-level languages (COBOL, FORTRAN), time-sharing |
| 4th | 1971–present | Microprocessors (VLSI) | Intel 4004, PC, Mac | Personal computers, GUI, internet |
| 5th | Present+ | AI / ULSI | AI systems | Artificial intelligence, voice recognition, parallel processing |
Types of Computers by Size
Supercomputer
Fastest, most expensive. Used in weather forecasting, nuclear research. India's: PARAM series (C-DAC).
Mainframe
Large, multi-user systems. Used by banks, airlines, government. IBM Z-series.
Minicomputer
Mid-sized. Used by departments. DEC PDP series.
Microcomputer / Personal Computer
Desktop, laptop, tablet. Most common. Based on microprocessor.
Hardware
Input Devices
Keyboard
Primary text input. QWERTY layout standard.
Mouse
Pointing device. Left click, right click, scroll.
Scanner
Converts physical documents to digital.
Microphone
Audio input.
Webcam
Video/image input.
Joystick
Used for games/aircraft simulation.
Light pen
Draws on screen directly.
Barcode reader
Reads barcodes (shops, libraries).
OCR
Optical Character Recognition — reads printed text.
Output Devices
Monitor
Primary visual output. CRT (old), LCD, LED, OLED.
Printer
Impact (Dot matrix), Non-impact (Inkjet, Laser). Laser = fastest, best quality.
Speakers
Audio output.
Plotter
Draws diagrams, engineering drawings. Large format.
Projector
Displays on large screen.
Headphones
Personal audio output.
CPU — Central Processing Unit
"Brain of the computer." Contains:
ALU (Arithmetic Logic Unit)
Performs arithmetic (+,-,×,÷) and logic (AND, OR, NOT) operations.
Control Unit (CU)
Directs and coordinates all computer operations. Fetches, decodes, executes instructions.
Registers
Temporary, fastest storage inside CPU. Stores data being processed right now.
Software
Types of Software
System Software
Manages hardware resources. Runs in background.
- Operating System (Windows, Linux, macOS)
- Device Drivers
- Utility programs (Antivirus, Disk cleanup)
- Language Translators
Application Software
Designed for end-user tasks.
- Word processors (MS Word)
- Spreadsheets (MS Excel)
- Databases (MS Access, MySQL)
- Presentation (MS PowerPoint)
- Web browsers (Chrome, Firefox)
Language Translators
| Translator | Function | Example |
|---|---|---|
| Compiler | Translates entire high-level program to machine code at once | C, C++ compilers |
| Interpreter | Translates and executes one line at a time | Python, JavaScript |
| Assembler | Translates assembly language to machine language | NASM, MASM |
Programming Languages (Generation)
| Generation | Language | Example |
|---|---|---|
| 1GL | Machine Language | Binary (0s and 1s) — directly understood by CPU |
| 2GL | Assembly Language | MOV, ADD — uses mnemonics, needs assembler |
| 3GL | High-Level Language | C, COBOL, FORTRAN, Pascal |
| 4GL | Very High-Level Language | SQL, MATLAB, R — closer to natural language |
| 5GL | AI/Natural Language | Prolog, Mercury — AI and constraint programming |
Memory & Storage
Memory Hierarchy
Fastest to slowest / Smallest to largest:
Registers → Cache → RAM → ROM → HDD/SSD → Optical disc → Magnetic tape
Primary Memory (Internal)
RAM — Random Access Memory
- Volatile — data lost when power off
- Read & Write
- Two types: DRAM (Dynamic), SRAM (Static)
- Working memory of computer
ROM — Read Only Memory
- Non-volatile — retains data permanently
- Read only (mostly)
- Types: PROM, EPROM, EEPROM
- Contains BIOS (Basic Input Output System)
Storage Units
| Unit | Abbreviation | Size |
|---|---|---|
| Bit | b | Smallest unit (0 or 1) |
| Nibble | — | 4 bits |
| Byte | B | 8 bits |
| Kilobyte | KB | 1024 Bytes |
| Megabyte | MB | 1024 KB |
| Gigabyte | GB | 1024 MB |
| Terabyte | TB | 1024 GB |
| Petabyte | PB | 1024 TB |
| Exabyte | EB | 1024 PB |
Secondary Storage
| Type | Technology | Typical Capacity |
|---|---|---|
| HDD (Hard Disk Drive) | Magnetic, spinning platters | 500GB – 4TB |
| SSD (Solid State Drive) | Flash memory, no moving parts | 128GB – 4TB |
| CD-ROM | Optical, laser read | 700MB |
| DVD | Optical, dual layer | 4.7GB – 17GB |
| Blu-ray | Optical, blue laser | 25GB – 100GB |
| Pen Drive / USB Flash | Flash memory | 4GB – 256GB |
| SD Card | Flash memory | 2GB – 1TB |
Operating System
What is an OS?
System software that acts as interface between user and hardware. Manages all resources.
Functions of OS
- Process management — manages running programs
- Memory management — allocates/deallocates RAM
- File management — organizes data in files and folders
- Device management — manages I/O devices via drivers
- Security & access control — user accounts, passwords
Types of OS
| Type | Description | Examples |
|---|---|---|
| Batch OS | Jobs processed in batches without user interaction | Early mainframe systems |
| Time-sharing OS | Multiple users share CPU time; fast switching | UNIX |
| Distributed OS | Multiple computers appear as one system | Google's Borg, Apache Mesos |
| Real-time OS (RTOS) | Processes in fixed time; used in critical systems | VxWorks, FreeRTOS |
| Network OS | Manages network resources | Windows Server, Novell NetWare |
| Mobile OS | For smartphones/tablets | Android (Google), iOS (Apple) |
Popular Operating Systems
Windows
Microsoft. GUI-based. Most used desktop OS. Windows 11 latest.
macOS
Apple. Unix-based. For Mac computers. Very secure.
Linux
Open-source. Many distros (Ubuntu, Fedora, Debian). Used in servers.
Android
Google. Linux-based. Most used mobile OS globally.
iOS
Apple. For iPhone/iPad. Closed ecosystem.
Chrome OS
Google. Linux-based. For Chromebooks. Cloud-focused.
Internet & Networking
Network Types
| Type | Full Name | Range | Example |
|---|---|---|---|
| PAN | Personal Area Network | ~10m | Bluetooth, USB |
| LAN | Local Area Network | Building/Campus | Office network, school lab |
| MAN | Metropolitan Area Network | City | Cable TV network |
| WAN | Wide Area Network | Country/World | Internet, SWIFT banking |
Network Topologies
Bus
All devices on a single cable. Simple but failure of main cable = failure of whole network.
Star
All devices connect to central hub/switch. Most common. Easy to add devices.
Ring
Devices in a circular chain. Token passing. Failure at one point affects all.
Mesh
Every device connected to every other. Most reliable but expensive.
Tree
Hierarchical. Combination of bus and star. Used in enterprise networks.
Hybrid
Combination of any two or more topologies. Most modern networks.
Key Internet Terms
| Term | Meaning |
|---|---|
| HTTP | HyperText Transfer Protocol — foundation of web browsing |
| HTTPS | HTTP + SSL/TLS encryption — secure web browsing |
| FTP | File Transfer Protocol — transferring files between computers |
| SMTP | Simple Mail Transfer Protocol — sending emails |
| POP3 | Post Office Protocol 3 — receiving emails (downloads to device) |
| IMAP | Internet Message Access Protocol — receiving emails (syncs with server) |
| DNS | Domain Name System — translates domain names to IP addresses |
| IP Address | Unique address of a device on network. IPv4 (32-bit), IPv6 (128-bit) |
| Router | Connects different networks; determines best path for data |
| Modem | Modulator-Demodulator — converts digital ↔ analog signals for ISP |
| ISP | Internet Service Provider — company providing internet access |
| URL | Uniform Resource Locator — full web address |
| HTML | HyperText Markup Language — language for web pages |
| WWW | World Wide Web — information system on the internet (≠ internet itself) |
| Browser | Software to access web. Chrome, Firefox, Safari, Edge. |
| Search Engine | Google, Bing, Yahoo — index and search web content |
MS Office Shortcuts
MS Word
MS Excel
MS PowerPoint
Number Systems
Types of Number Systems
| System | Base | Digits Used |
|---|---|---|
| Binary | 2 | 0, 1 |
| Octal | 8 | 0 – 7 |
| Decimal | 10 | 0 – 9 |
| Hexadecimal | 16 | 0–9 and A(10), B(11), C(12), D(13), E(14), F(15) |
Binary Conversions
| Decimal | Binary | Decimal | Binary |
|---|---|---|---|
| 0 | 0000 | 8 | 1000 |
| 1 | 0001 | 9 | 1001 |
| 2 | 0010 | 10 | 1010 |
| 3 | 0011 | 11 | 1011 |
| 4 | 0100 | 12 | 1100 |
| 5 | 0101 | 13 | 1101 |
| 6 | 0110 | 14 | 1110 |
| 7 | 0111 | 15 | 1111 |
Decimal → Binary Conversion
Divide by 2 repeatedly, write remainders bottom to top.
Example: 13 → 13÷2=6 R1, 6÷2=3 R0, 3÷2=1 R1, 1÷2=0 R1 → Read bottom to top: 1101
Binary → Decimal Conversion
Which key combination is used to open the Find and Replace dialog in MS Word?Direct shortcut question
The decimal equivalent of binary number 1010 is?
RAM is an example of which type of memory?Memory classification