Basics of Computer — GS Notes for EPFO, DRDO SAO, BPSC, RBI & PFRDA
Hardware, memory, software, MS Office shortcuts, networking, cyber security and emerging tech — compressed into exam-ready tables with practice MCQs.
Quick Facts
- IPO(S) cycle: Input → Process → Output (+ Storage).
- Speed order: Registers > Cache > RAM > SSD > HDD.
- IPv4 32-bit · IPv6 128-bit · MAC 48-bit.
- PARAM 8000 (1991, C-DAC) — India’s first supercomputer.
- CERT-In handles cyber incidents; IT Act 2000 is the core cyber law.
What a computer is (and the exam definition)
A computer is an electronic device that takes input, processes it according to instructions (a program), stores data and results, and produces output. This is the IPO(S) cycle. Charles Babbage is called the “father of the computer” for his Analytical Engine design. Ada Lovelace is called the first programmer.
| Unit | Role | Examples |
|---|---|---|
| Input | Feeds data/instructions | Keyboard, mouse, scanner, microphone, webcam, OMR/OCR/MICR readers, barcode reader |
| Processing (CPU) | Executes instructions | ALU + Control Unit + registers |
| Memory / Storage | Holds data & programs | RAM, ROM, cache, SSD/HDD |
| Output | Presents results | Monitor, printer, speaker, projector, plotter |
Syllabus link: “General Science and Basic Knowledge of Computer Applications” (UPSC EPFO) and “Fundamentals of Computer Application” (DRDO SAO RT). See APFC 2026 syllabus & exam pattern and DRDO SAO syllabus.
Generations of computers
| Generation | Period (approx.) | Technology | Example |
|---|---|---|---|
| First | 1940s–1956 | Vacuum tubes | ENIAC, UNIVAC |
| Second | 1956–1963 | Transistors | IBM 1401 |
| Third | 1964–1971 | Integrated circuits (ICs) | IBM System/360 |
| Fourth | 1971–present | Microprocessors (VLSI) | Personal computers |
| Fifth | Present & beyond | AI, parallel processing, ULSI, quantum research | AI systems |
India’s first indigenous supercomputer: PARAM 8000 (1991), built by C-DAC.
CPU, memory hierarchy and units
| Component | Key fact |
|---|---|
| ALU | Does arithmetic and logical operations |
| Control Unit | Directs the flow of instructions and data |
| Registers | Fastest, smallest storage inside the CPU |
| Cache | Very fast memory between the CPU and RAM (L1/L2/L3) |
| RAM | Volatile primary memory — lost when power goes off (DRAM, SRAM) |
| ROM | Non-volatile; holds firmware/BIOS (PROM, EPROM, EEPROM) |
| Secondary storage | HDD, SSD, optical (CD/DVD/Blu-ray), pen drives — non-volatile |
| Speed order | Registers > Cache > RAM > SSD > HDD |
| Unit | Equals |
|---|---|
| 1 nibble | 4 bits |
| 1 byte | 8 bits |
| 1 KB | 1024 bytes |
| 1 MB | 1024 KB |
| 1 GB | 1024 MB |
| 1 TB | 1024 GB |
| 1 PB | 1024 TB |
| 1 EB | 1024 PB |
| 1 ZB | 1024 EB |
| 1 YB | 1024 ZB |
Software types
| Type | Meaning | Examples |
|---|---|---|
| System software | Runs the hardware | Operating systems (Windows, Linux, macOS, Android), device drivers |
| Utility software | Maintenance | Antivirus, disk cleanup, compression tools |
| Application software | User tasks | MS Office, browsers, Tally, Photoshop |
| Language translators | Convert code to machine code | Compiler (whole program), Interpreter (line by line), Assembler (assembly → machine code) |
| Open source | Source code freely available | Linux, LibreOffice, Firefox |
| Firmware | Software stored on hardware | BIOS/UEFI |
Languages: machine language (binary) → assembly (mnemonics) → high-level (C, C++, Java, Python). BPSC’s 69th Prelims final key had a programming-language identification question (Cobra, Python, Squirrel) — see the 69th solved paper.
Operating system essentials
- The OS manages processes, memory, files, devices and security, and provides the user interface (CLI or GUI).
- Booting: cold boot (from power-off) vs warm boot (restart).
- Types: batch, time-sharing, real-time (RTOS), distributed, mobile.
- File systems: FAT32, NTFS (Windows), ext4 (Linux), APFS (macOS).
MS Office & shortcuts (high-yield)
| Shortcut | Action |
|---|---|
| Ctrl+C / Ctrl+X / Ctrl+V | Copy / Cut / Paste |
| Ctrl+Z / Ctrl+Y | Undo / Redo |
| Ctrl+S | Save |
| Ctrl+P | |
| Ctrl+F / Ctrl+H | Find / Replace |
| Ctrl+A | Select all |
| Ctrl+B / I / U | Bold / Italic / Underline |
| F7 (Word) | Spelling & grammar |
| F5 (PowerPoint) | Start slideshow from beginning |
| F2 (Excel) | Edit active cell |
| Ctrl+; (Excel) | Insert today’s date |
| Alt+F4 | Close the active window |
| Windows+L | Lock the computer |
| Windows+D | Show desktop |
| Excel concept | Fact |
|---|---|
| Cell address | Column letter + row number (e.g., B7) |
| Formula start | Always with = |
| Common functions | SUM, AVERAGE, COUNT, COUNTA, IF, VLOOKUP/XLOOKUP, CONCAT |
| Absolute reference | $A$1 does not change when copied |
| File extensions | Word .docx, Excel .xlsx, PowerPoint .pptx |
Networking & Internet
| Term | Meaning |
|---|---|
| LAN / MAN / WAN | Local / Metropolitan / Wide area networks |
| PAN | Personal area network (Bluetooth) |
| Topologies | Bus, star, ring, mesh, tree, hybrid |
| IP address | IPv4 = 32-bit; IPv6 = 128-bit |
| MAC address | 48-bit hardware address of a network card |
| DNS | Translates domain names to IP addresses |
| HTTP / HTTPS | Web protocols; HTTPS is encrypted with TLS |
| FTP | File transfer |
| SMTP / POP3 / IMAP | Send email / download email / sync email |
| Router / Switch / Hub | Route between networks / smart LAN forwarding / broadcast to all ports |
| Modem | Modulator–demodulator |
| URL | Uniform Resource Locator |
| Cloud models | IaaS, PaaS, SaaS |
| WWW inventor | Tim Berners-Lee (1989, CERN) |
| ARPANET | Precursor of the Internet (1969) |
Cyber security vocabulary
| Threat / term | What it is |
|---|---|
| Virus | Attaches to files and needs a host to spread |
| Worm | Self-replicates across networks without a host |
| Trojan | Disguised as legitimate software |
| Ransomware | Encrypts data and demands payment |
| Phishing | Fraudulent messages that steal credentials |
| Spyware / Keylogger | Secretly monitors or records keystrokes |
| DDoS | Floods a service with traffic |
| Firewall | Filters network traffic by rules |
| Two-factor authentication | Something you know + something you have/are |
| Encryption | Converts plaintext to ciphertext |
| CERT-In | India’s national nodal agency for cyber incidents (under MeitY) |
| IT Act, 2000 | India’s primary cyber law (amended 2008) |
Emerging tech (CA overlap)
| Term | One-liner |
|---|---|
| AI / ML | Machines that learn patterns from data |
| Generative AI | Creates text/images; GPT = Generative Pre-trained Transformer (asked in BPSC 69th) |
| IoT | Network of connected devices |
| Edge computing | Processing near the data source |
| 5G network slicing | Several virtual networks on one physical infrastructure |
| Blockchain | Distributed, tamper-evident ledger |
| Quantum computing | Uses qubits; India’s National Quantum Mission approved in 2023 |
| Digital Public Infrastructure | Aadhaar, UPI, DigiLocker, ONDC — India’s DPI stack |
Must-know abbreviations
| Abbreviation | Full form |
|---|---|
| CPU | Central Processing Unit |
| GPU | Graphics Processing Unit |
| RAM | Random Access Memory |
| ROM | Read Only Memory |
| BIOS | Basic Input Output System |
| USB | Universal Serial Bus |
| HTML | HyperText Markup Language |
| Portable Document Format | |
| OCR | Optical Character Recognition |
| MICR | Magnetic Ink Character Recognition (cheques) |
| OMR | Optical Mark Recognition |
| ASCII | American Standard Code for Information Interchange |
| VPN | Virtual Private Network |
| SSD | Solid State Drive |
Practice MCQs
- Which memory is volatile? (a) ROM (b) RAM (c) SSD (d) EEPROM — (b)
- IPv6 addresses are — (a) 32-bit (b) 64-bit (c) 128-bit (d) 256-bit — (c)
- Which translates a whole program at once? (a) Interpreter (b) Compiler (c) Assembler (d) Loader — (b)
- MICR technology is mainly used in — (a) Exams (b) Banks/cheques (c) Libraries (d) Retail — (b)
- 1 TB equals — (a) 1024 MB (b) 1024 GB (c) 1000 KB (d) 1024 PB — (b)
- India’s first supercomputer PARAM 8000 was developed by — (a) ISRO (b) C-DAC (c) DRDO (d) BARC — (b)
Exam strategy for the computer section
Computer questions are among the most scoring in UPSC EPFO, DRDO SAO, banking and PSC papers, because the static base barely changes. Typical pattern:
- 2–4 questions on memory, units and hardware.
- 1–3 on software types, OS and programming-language basics.
- 1–2 on MS Office features and shortcuts.
- 1–3 on networking, internet protocols and abbreviations.
- 1–2 on cyber security and current tech (AI, 5G, IoT, quantum).
Plan: 3 days to read these notes twice, 2 days of 100+ MCQs, then 20 MCQs a week as maintenance. Use the CA hub for new tech terms.
Commonly confused pairs
| Pair | Difference |
|---|---|
| RAM vs ROM | Volatile working memory vs non-volatile firmware memory |
| Compiler vs Interpreter | Whole program at once vs line by line |
| Virus vs Worm | Needs a host file vs spreads by itself |
| Hub vs Switch | Broadcasts to all ports vs sends to the right port |
| HTTP vs HTTPS | Plain vs encrypted (TLS) |
| Internet vs WWW | The network vs the hypertext service that runs on it |
| Bit vs Byte | Single binary digit vs 8 bits |
Number systems & logic gates
Number-system conversion is a frequent 1-mark question in banking and SSC-style papers, and it occasionally appears in UPSC RT computer sections.
| System | Base | Digits | Example |
|---|---|---|---|
| Binary | 2 | 0, 1 | 1010₂ = 10₁₀ |
| Octal | 8 | 0–7 | 12₈ = 10₁₀ |
| Decimal | 10 | 0–9 | 10 |
| Hexadecimal | 16 | 0–9, A–F | A₁₆ = 10₁₀ |
Quick method: decimal → binary by repeated division by 2 (read remainders bottom-up); binary → decimal by place values (8-4-2-1). Group binary digits in 3s for octal and 4s for hex.
| Gate | Output rule | Universal? |
|---|---|---|
| AND | 1 only if all inputs are 1 | No |
| OR | 1 if any input is 1 | No |
| NOT | Inverts input | No |
| NAND | Inverse of AND | Yes — universal gate |
| NOR | Inverse of OR | Yes — universal gate |
| XOR | 1 if inputs differ | No |
Storage & device facts
- CD ≈ 700 MB; single-layer DVD ≈ 4.7 GB; single-layer Blu-ray ≈ 25 GB.
- SSDs have no moving parts, so they are faster and more shock-resistant than HDDs.
- Impact printers (dot-matrix) vs non-impact printers (inkjet, laser). Plotters are used for large engineering drawings.
- A touchscreen display is both an input and an output device.
Computing milestones timeline
| Year | Milestone |
|---|---|
| 1822–1837 | Babbage’s Difference Engine and Analytical Engine designs |
| 1946 | ENIAC — early general-purpose electronic computer |
| 1947 | Transistor invented at Bell Labs |
| 1958–59 | Integrated circuit (Kilby, Noyce) |
| 1969 | ARPANET goes live |
| 1971 | Intel 4004 — first commercial microprocessor |
| 1981 | IBM PC launched |
| 1989 | World Wide Web proposed by Tim Berners-Lee |
| 1991 | PARAM 8000 by C-DAC (India); Linux kernel released |
| 1995 | Public Internet access in India via VSNL (15 August 1995) |
| 2016 | UPI launched by NPCI |
Timeline questions are rare, but the India-specific rows (PARAM, VSNL, UPI) come up in BPSC and banking GA.
Score full marks in the computer section
Topic-wise computer MCQ sets inside CrackTarget test series.
Take a free UPSC EPFO mock test →Frequently Asked Questions
Is computer knowledge part of the UPSC EPFO syllabus?
Yes. The syllabus includes “General Science and Basic Knowledge of Computer Applications”. DRDO SAO’s RT includes “Fundamentals of Computer Application”.
What is the difference between RAM and ROM?
RAM is volatile working memory that loses data without power; ROM is non-volatile and stores firmware such as BIOS.
What is the difference between a compiler and an interpreter?
A compiler translates the whole program into machine code before execution; an interpreter translates and executes line by line.
Which body handles cyber incidents in India?
CERT-In (Indian Computer Emergency Response Team) under MeitY is the national nodal agency.
How much computer knowledge is enough for these exams?
Fundamentals, MS Office, networking, internet, cyber security and current tech terms — about 20–25 study hours plus regular MCQ practice.
Last updated October 2026. Standard computer fundamentals; India-specific items (C-DAC PARAM, CERT-In, IT Act, National Quantum Mission) are well established.