In this guide
In the IBPS PO mains, computer aptitude does not have a section of its own. It shares the "Reasoning & Computer Aptitude" section, so every computer question you answer in thirty seconds buys time for a long puzzle. That is the real reason to prepare it: not because it is heavy, but because it is fast.
Most questions are direct recall ("which layer does a router work at?") or a small calculation ("convert 2F to decimal"). A week of notes plus regular quizzes covers most of it.
Hardware and memory
- The CPU has an arithmetic logic unit (ALU) for calculations and comparisons, a control unit (CU) that directs the steps, and registers, the fastest storage of all.
- Primary memory is the memory the CPU works with directly: RAM and ROM. Secondary storage keeps data long-term: hard disks, SSDs, pen drives, optical discs.
- RAM is volatile; it loses data when power goes. ROM is non-volatile.
| Memory, fastest to slowest | Notes |
|---|---|
| Registers | Inside the CPU |
| Cache | Usually SRAM; holds data the CPU needs next |
| Main memory (RAM) | Usually DRAM; needs constant refreshing |
| Secondary storage | SSD faster than a hard disk; both far slower than RAM |
Kinds of ROM: PROM can be written once; EPROM is erased with ultraviolet light; EEPROM is erased electrically. Flash memory, used in pen drives and SSDs, is a form of EEPROM.
Units: 1 nibble = 4 bits; 1 byte = 8 bits. In exam questions, 1 KB = 1,024 bytes, 1 MB = 1,024 KB, and so on through GB, TB and PB.
Number systems
| System | Base | Digits used |
|---|---|---|
| Binary | 2 | 0, 1 |
| Octal | 8 | 0–7 |
| Decimal | 10 | 0–9 |
| Hexadecimal | 16 | 0–9 and A–F (A = 10 … F = 15) |
Worked conversions
Decimal 45 to binary. Divide by 2 and read the remainders from bottom to top.
- 45 ÷ 2 = 22 r 1; 22 ÷ 2 = 11 r 0; 11 ÷ 2 = 5 r 1; 5 ÷ 2 = 2 r 1; 2 ÷ 2 = 1 r 0; 1 ÷ 2 = 0 r 1.
- Bottom to top: 101101. Check: 32 + 8 + 4 + 1 = 45.
Binary 101101 to octal and hexadecimal. Group bits from the right.
- Groups of three for octal: 101 101 → 5 5 → 55 (5 × 8 + 5 = 45).
- Groups of four for hex: 0010 1101 → 2 D → 2D (2 × 16 + 13 = 45).
Hexadecimal 2F to decimal. 2 × 16 + 15 = 47. Octal 57 to decimal: 5 × 8 + 7 = 47.
Binary addition. 1011 + 0110 = 10001. Check: 11 + 6 = 17, and 10001 is 16 + 1.
Logic gates
| Gate | Output is 1 when |
|---|---|
| AND | All inputs are 1 |
| OR | At least one input is 1 |
| NOT | The single input is 0 |
| NAND | Not all inputs are 1 |
| NOR | All inputs are 0 |
| XOR | The two inputs differ |
NAND and NOR are called universal gates, because every other gate can be built from either one.
Software basics
- System software runs the machine (operating system, device drivers, utilities). Application software does a user's task (word processor, browser, banking app).
- A compiler translates a whole program into machine code before it runs. An interpreter translates and runs it line by line. An assembler converts assembly language into machine code.
Networks
- PAN (a few metres, for example Bluetooth), LAN (a building or campus), MAN (a city), WAN (a country or the world; the internet is the largest WAN).
- Topologies: bus (one shared cable), star (all nodes to a central switch or hub), ring, mesh and tree. A full mesh of n devices needs n(n − 1)/2 links; for 5 devices that is 10.
- An IPv4 address is 32 bits, written as four decimal numbers (for example 192.168.1.10). An IPv6 address is 128 bits, written in hexadecimal groups. A MAC address is 48 bits and identifies a network card.
- DNS turns a domain name into an IP address.
The OSI model
| Layer | Name | Job | Examples |
|---|---|---|---|
| 7 | Application | Services for the user | HTTP, FTP, SMTP, DNS |
| 6 | Presentation | Format, encryption, compression | Data translation |
| 5 | Session | Opens and manages sessions | Session control |
| 4 | Transport | End-to-end delivery | TCP, UDP |
| 3 | Network | Routing, logical addressing | IP, routers |
| 2 | Data Link | Framing, physical (MAC) addressing | Switches, bridges |
| 1 | Physical | Bits over the medium | Cables, hubs, repeaters |
TCP is connection-oriented and resends lost data. UDP is connectionless and faster, used where speed matters more than a lost packet, such as live video. The TCP/IP model is usually taught with four layers; some books use five, so read the options carefully.
Common ports
| Protocol | Port | Use |
|---|---|---|
| FTP | 20, 21 | File transfer (data, control) |
| SSH | 22 | Secure remote login |
| Telnet | 23 | Unencrypted remote login |
| SMTP | 25 | Sending email |
| DNS | 53 | Name resolution |
| HTTP | 80 | Web pages |
| POP3 | 110 | Downloading email |
| IMAP | 143 | Reading email on the server |
| HTTPS | 443 | Secure web pages |
Databases
- A DBMS stores and manages data; in a relational DBMS, data sits in tables of rows (records, tuples) and columns (fields, attributes).
- A primary key uniquely identifies each row and cannot be empty. A foreign key in one table refers to the primary key of another. A candidate key is any column set that could serve as the primary key.
- Normalisation splits tables to reduce repeated data.
- SQL commands: DDL defines structure (CREATE, ALTER, DROP, TRUNCATE); DML handles data (INSERT, UPDATE, DELETE, and SELECT, which some books list separately as DQL); DCL controls access (GRANT, REVOKE); TCL handles transactions (COMMIT, ROLLBACK).
MS Office shortcuts
| Shortcut | Action |
|---|---|
| Ctrl + N, O, S, P | New, open, save, print |
| Ctrl + Z / Ctrl + Y | Undo / redo |
| Ctrl + F / Ctrl + H | Find / replace |
| Ctrl + K | Insert hyperlink |
| Ctrl + L, E, R, J (Word) | Align left, centre, right, justify |
| F7 (Word) | Spelling and grammar |
| F12 (Word) | Save As |
| Shift + F3 (Word) | Change case |
| F5 / Shift + F5 (PowerPoint) | Slide show from the start / from the current slide |
| F2 (Excel) | Edit the active cell |
| Ctrl + ; (Excel) | Insert today's date |
| F4 (Excel, while editing a formula) | Cycle through absolute and relative references, for example A1 to $A$1 |
Security
| Term | Meaning |
|---|---|
| Virus | Attaches to a host file and spreads when that file runs |
| Worm | Copies itself across networks without needing a host file |
| Trojan | Harmful program disguised as a useful one |
| Ransomware | Locks or encrypts data and demands payment |
| Spyware / keylogger | Secretly records activity or keystrokes |
| Phishing / vishing / smishing | Fraud through email or fake sites / voice calls / SMS |
| Firewall | Filters network traffic by rules |
| DDoS | Floods a service from many machines so real users cannot reach it |
| Symmetric encryption | One shared key encrypts and decrypts |
| Asymmetric encryption | A public key and a private key; what one locks, only the other opens |
| Digital signature | Signed with the sender's private key, verified with their public key |
| Two-factor authentication | A second proof, such as an OTP, on top of a password |
Practice set
- Convert decimal 29 to binary.
- What is hexadecimal 3C in decimal?
- At which OSI layer does a router work?
- Which port does SMTP use by default?
- Which gate gives output 1 only when its two inputs differ?
- How many bits are in an IPv6 address?
- Which SQL command removes a table completely, structure included?
- Which key starts a PowerPoint slide show from the current slide?
- Which malware spreads across a network without attaching to a host file?
- How many links does a full mesh of 6 devices need?
Answers
- 11101. 16 + 8 + 4 + 1 = 29.
- 60. 3 × 16 + 12 = 60.
- Network layer (layer 3).
- 25.
- XOR.
- 128.
- DROP. DELETE removes rows; TRUNCATE empties the table but keeps its structure.
- Shift + F5.
- A worm.
- 15. 6 × 5 ÷ 2 = 15.
What to do next
- Copy the OSI and port tables by hand once, then quiz yourself from memory the next day.
- Do five conversions a day for a week, mixing all four bases.
- Take one 20-question computer quiz each week of the mains phase, and read mains reasoning for where these questions fit in your section time.
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 Institute of Banking Personnel Selection website .
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