In this guide
In the SBI PO mains, computer questions are part of the Reasoning & Computer Aptitude section. Most of them are factual: you either know what a router does or you don't. That makes them the fastest marks in the section, a few seconds each, and they buy you time for the puzzles that follow. The number of computer questions varies from paper to paper.
This guide gives you the core facts topic by topic, with the conversions worked out, so you can build a one-page revision sheet from it.
Topics that repeat
| Topic | What is usually asked |
|---|---|
| Hardware | Input and output devices; parts of the CPU |
| Memory | RAM vs ROM; cache; types of ROM; storage units |
| Number systems | Binary, octal, decimal and hexadecimal conversions |
| Software | System vs application software; compilers and interpreters |
| Networking | LAN, MAN, WAN; hub, switch, router, modem; OSI layers |
| Internet | Protocols, IP addresses, URLs, email |
| Security | Virus, worm, trojan, ransomware, phishing, firewall |
| Databases | Keys, records and fields, SQL command groups |
| MS Office | Shortcuts; Excel formulas and cell references |
| Abbreviations | BIOS, USB, OCR, MICR, UPS and many more |
Hardware and the CPU
The CPU has three main parts: the ALU (arithmetic and logic operations), the control unit (directs the flow of data and instructions) and registers (tiny, very fast storage inside the processor).
- Input devices: keyboard, mouse, scanner, microphone, webcam, barcode reader, MICR and OMR readers.
- Output devices: monitor, printer, speaker, projector, plotter.
- Both: touchscreen, and a modem, which both sends and receives.
Memory
| Memory | Key facts |
|---|---|
| Registers | Inside the CPU; the fastest and smallest |
| Cache | Between the CPU and RAM; holds frequently used data; usually SRAM |
| RAM | Main memory; volatile (loses data when power is off); usually DRAM |
| ROM | Non-volatile; holds start-up instructions |
| Secondary storage | Hard disk, SSD, pen drive; non-volatile and large |
Speed runs from fastest to slowest in the order of the table; capacity runs the other way.
Types of ROM: PROM (programmed once), EPROM (erased with ultraviolet light), EEPROM (erased electrically). Flash memory is a type of EEPROM.
Units: 1 nibble = 4 bits; 1 byte = 8 bits; 1 KB = 1,024 bytes; then MB, GB, TB and PB, each 1,024 times the one before.
Number systems
| System | Base | Digits used |
|---|---|---|
| Binary | 2 | 0, 1 |
| Octal | 8 | 0 to 7 |
| Decimal | 10 | 0 to 9 |
| Hexadecimal | 16 | 0 to 9, then A to F (A = 10 … F = 15) |
Worked conversions:
- Decimal 45 to binary: 45 = 32 + 8 + 4 + 1, so the 32, 8, 4 and 1 places are 1 and the 16 and 2 places are 0. 101101.
- Decimal 255 to hexadecimal: 255 = 15 × 16 + 15. FF. In octal, 255 = 3 × 64 + 7 × 8 + 7, which is 377.
- Hexadecimal 2F to decimal: 2 × 16 + 15 = 47.
- Binary 11001 to decimal: 16 + 8 + 1 = 25.
- Binary addition: 1011 + 0110. That is 11 + 6 = 17, which is 10001 in binary.
Software
- System software runs the computer: the operating system, device drivers and utilities.
- Application software does a user's task: word processors, spreadsheets, browsers.
- Compiler: translates a whole program into machine code before it runs.
- Interpreter: translates and runs a program one line at a time.
- Assembler: translates assembly language into machine code.
- Operating system jobs: managing memory, processes, files and devices, and providing the user interface.
- Booting: a cold boot starts the computer from power-off; a warm boot restarts it while it is on.
Networking and the internet
| Device | What it does | OSI layer |
|---|---|---|
| Hub | Sends incoming data to every connected device | 1, Physical |
| Switch | Sends data only to the intended device, using MAC addresses | 2, Data Link |
| Router | Forwards data between networks, using IP addresses | 3, Network |
| Modem | Converts digital signals to analog and back | Physical |
OSI model, bottom to top: Physical, Data Link, Network, Transport, Session, Presentation, Application.
Network sizes: a LAN covers a building or campus, a MAN a city, and a WAN a country or the world. The internet is the largest WAN.
Addresses: an IPv4 address is 32 bits long; IPv6 is 128 bits; a MAC address is 48 bits.
| Protocol | Job | Common port |
|---|---|---|
| HTTP | Web pages | 80 |
| HTTPS | Secure web pages | 443 |
| FTP | File transfer | 20 and 21 |
| SMTP | Sending email | 25 |
| POP3 | Receiving email (downloads it) | 110 |
| IMAP | Receiving email (keeps it on the server) | 143 |
| DNS | Turns domain names into IP addresses | 53 |
Security
| Threat or tool | What it is |
|---|---|
| Virus | Attaches to a file or program and spreads when it is run |
| Worm | Copies itself across networks without needing a host file |
| Trojan | Malware disguised as useful software |
| Ransomware | Encrypts files and demands payment to unlock them |
| Spyware and keyloggers | Secretly record activity or keystrokes |
| Phishing | Fake emails or websites that trick people into giving details; vishing uses calls, smishing uses SMS |
| Firewall | Monitors and filters network traffic by rules |
| Encryption | Scrambles data so only someone with the key can read it |
Databases
- A table holds records (rows, also called tuples) and fields (columns, also called attributes).
- A primary key uniquely identifies each record and cannot be empty.
- A foreign key in one table refers to the primary key of another, linking the two.
- SQL command groups: DDL defines structure (CREATE, ALTER, DROP, TRUNCATE); DML changes data (INSERT, UPDATE, DELETE); DCL controls access (GRANT, REVOKE); TCL manages transactions (COMMIT, ROLLBACK). SELECT is placed under DML in some books and under a separate DQL group in others.
MS Office shortcuts
These are for Microsoft Office on Windows. Some differ between versions and on a Mac.
| Shortcut | Action |
|---|---|
| Ctrl + Z / Ctrl + Y | Undo / redo |
| Ctrl + B, I, U | Bold, italic, underline |
| Ctrl + E, L, R, J | Centre, left, right, justify (Word) |
| Ctrl + K | Insert a hyperlink |
| F7 | Spelling and grammar check (Word) |
| F12 | Save As |
| F5 / Shift + F5 | Slide show from the beginning / from the current slide (PowerPoint) |
| F2 | Edit the active cell (Excel) |
| Ctrl + ; | Insert today's date (Excel) |
| Alt + = | AutoSum (Excel) |
Excel references: A1 is relative and changes when a formula is copied. $A$1 is absolute and stays fixed. $A1 and A$1 are mixed. Every formula starts with =.
Abbreviations worth knowing
| Short form | Full form |
|---|---|
| ALU | Arithmetic Logic Unit |
| BIOS | Basic Input/Output System |
| DNS | Domain Name System |
| GUI | Graphical User Interface |
| MICR | Magnetic Ink Character Recognition (used on cheques) |
| OCR | Optical Character Recognition |
| OMR | Optical Mark Recognition |
| UPS | Uninterruptible Power Supply |
| URL | Uniform Resource Locator |
| USB | Universal Serial Bus |
| VPN | Virtual Private Network |
A two-week plan
| Days | Topics |
|---|---|
| 1–3 | Hardware, memory, number systems (do ten conversions a day) |
| 4–6 | Software, operating systems, MS Office |
| 7–9 | Networking, internet, email |
| 10–11 | Security, databases |
| 12–14 | Abbreviations, previous papers, a 20-question quiz each day |
About 30 to 40 minutes a day is enough. After that, revise the sheet once a week.
Self-test
- Which memory is volatile, RAM or ROM?
- Which protocol sends email?
- What is 13 in binary?
- Which key starts a PowerPoint slide show from the beginning?
- In a database table, what uniquely identifies each record?
- Which malware spreads across a network by itself?
- Which device forwards data between different networks?
- What is hexadecimal 3A in decimal?
- How many bits long is an IPv6 address?
Answers:
- RAM.
- SMTP.
- 1101. 8 + 4 + 1 = 13.
- F5.
- The primary key.
- A worm.
- A router.
- 58. 3 × 16 + 10 = 58.
- 128.
What to do next
- Turn the tables above into a one-page sheet and read it before every mains mock.
- Do ten number-system conversions a day until you never need to check them.
- In mocks, answer the computer questions first and note how long they take. Aim to finish them in five to six minutes.
- See the reasoning plan for where this fits, and digital banking for the banking-technology side.
A note on dates and numbers. Exam patterns, vacancies and schedules change from year to year. Always confirm the current details in the latest notification on the State Bank of India website .
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