Computer Knowledge

1. Computer Fundamentals: Hardware, Software, Memory and Number Systems

Computer Knowledge questions are mostly direct facts. This lesson covers the basics that appear in almost every paper: generations, parts of a computer, input and output devices, memory units and number systems.

History and generations

• Charles Babbage is called the 'Father of the Computer'. He designed the Analytical Engine in the 1830s.
• ENIAC (1945) was an early general-purpose electronic digital computer. UNIVAC I (1951) was an early commercial computer.
• First generation (about 1940-1956): vacuum tubes. Second generation (about 1956-1963): transistors.
• Third generation (about 1964-1971): integrated circuits (ICs). Fourth generation (1971 onwards): microprocessors.
• Fifth generation: based on artificial intelligence (AI) and parallel processing; still developing.

Hardware, software and the CPU

• Hardware is the physical parts you can touch. Software is the set of programs that tells the hardware what to do.
• System software runs the computer (operating system, device drivers, utilities). Application software does user tasks (MS Word, browsers, Tally).
• The CPU (Central Processing Unit) is the 'brain' of the computer. It has the ALU (Arithmetic Logic Unit), the CU (Control Unit) and registers.
• Input devices: keyboard, mouse, scanner, microphone, webcam, barcode reader, OMR, MICR (used for cheques), light pen, joystick.
• Output devices: monitor, printer, speaker, projector, plotter. A touch screen is both input and output.
• A compiler translates the whole program at once; an interpreter translates line by line; an assembler converts assembly language to machine code.

Memory and storage

• Primary memory: RAM is volatile (data is lost when power goes off); ROM is non-volatile (keeps data, e.g. the start-up firmware).
• Cache memory is a small, very fast memory between the CPU and RAM. Registers inside the CPU are the fastest of all.
• Secondary storage keeps data permanently: hard disk (HDD, magnetic), SSD and pen drive (flash memory), CD/DVD/Blu-ray (optical).
• Units: 1 bit = 0 or 1; 4 bits = 1 nibble; 8 bits = 1 byte.
• 1 KB = 1024 bytes; 1 MB = 1024 KB; 1 GB = 1024 MB; 1 TB = 1024 GB; 1 PB = 1024 TB (the convention used in exams).

Number systems basics

• Binary is base 2 (digits 0, 1). Octal is base 8 (0-7). Decimal is base 10 (0-9). Hexadecimal is base 16 (0-9 and A-F, where A = 10 and F = 15).
• Binary to decimal: multiply each digit by its place value (1, 2, 4, 8, 16 ... from the right). Example: 1101 = 8 + 4 + 0 + 1 = 13.
• Decimal to binary: divide by 2 again and again and read the remainders from bottom to top. Example: 10 = 1010.
• Computers work in binary because electronic circuits have two states: on (1) and off (0).

💡 Memorise the memory ladder in order: bit, nibble, byte, KB, MB, GB, TB, PB. Each step after byte is x 1024 in exam questions.

📝 5-question quiz on this lesson: enrol free to take it and track your score.

2. Operating Systems, Windows, File Management and Shortcuts

The operating system (OS) is the most important system software. It starts the computer and manages hardware, files and programs. Exams ask about OS basics, Windows features and keyboard shortcuts.

Operating system basics

• An OS manages memory, the processor, devices and files, and gives a user interface.
• Examples: Windows and macOS (desktop), Linux (open source), Android and iOS (mobile).
• GUI (Graphical User Interface) uses icons, windows and a mouse. CLI (Command Line Interface) uses typed commands, as in MS-DOS.
• Booting means starting the computer. A cold boot starts from power off; a warm boot is a restart.
• The BIOS or UEFI firmware runs first when the computer starts and then loads the OS.

Windows and file management

• The desktop is the main screen. The taskbar shows open programs; the Start button opens the Start menu.
• File Explorer is used to open, copy, move, rename and delete files and folders.
• A folder holds files and other folders. A file name has an extension that shows its type: .txt, .exe, .jpg, .pdf, .mp3, .zip.
• Deleted files go to the Recycle Bin and can be restored. Shift + Delete removes them without using the Recycle Bin.
• Files deleted from a pen drive or network drive usually do not go to the Recycle Bin.

Windows keyboard shortcuts

• Ctrl + C copy, Ctrl + X cut, Ctrl + V paste, Ctrl + Z undo, Ctrl + Y redo, Ctrl + A select all.
• Alt + Tab switches between open apps. Alt + F4 closes the active app.
• Windows key + D shows the desktop; Windows key + E opens File Explorer; Windows key + L locks the PC.
• Windows key + R opens Run; Windows key + I opens Settings; Ctrl + Shift + Esc opens Task Manager.
• F2 renames the selected file; F5 refreshes; Ctrl + Shift + N creates a new folder in File Explorer.
• Windows key + Shift + S takes a screenshot of part of the screen; Windows key + V opens clipboard history (it must first be turned on in Settings).

💡 Practise each shortcut on a real computer a few times. Shortcuts you have used are much easier to recall in the exam than ones you only read.

📝 5-question quiz on this lesson: enrol free to take it and track your score.

3. MS Word, Excel and PowerPoint

Microsoft Office is used in almost every government office. Exams ask about features, Excel functions, file extensions and shortcuts in Word, Excel and PowerPoint.

MS Word

• Word is a word processor. Its default file extension is .docx (Word 2007 onwards); the old format is .doc. Templates use .dotx.
• Ctrl + B bold, Ctrl + I italic, Ctrl + U underline. Ctrl + E centre, Ctrl + L left, Ctrl + R right, Ctrl + J justify.
• Ctrl + F find (opens the Navigation pane), Ctrl + H replace, Ctrl + K insert hyperlink, Ctrl + Enter page break, F7 spelling and grammar check, F12 Save As.
• Mail Merge creates many personalised letters or labels from one document and a list of names and addresses.
• Header and footer appear at the top and bottom of every page. Track Changes records edits made by reviewers.

MS Excel

• Excel is a spreadsheet. A workbook (.xlsx) contains worksheets made of cells. A cell address is column letter + row number, e.g. B3.
• Every formula starts with =. SUM adds, AVERAGE gives the mean, MAX and MIN give the largest and smallest, COUNT counts cells with numbers.
• IF tests a condition: =IF(B2>=35,"Pass","Fail").
• VLOOKUP looks up a value in the first column of a table and returns a value from another column: =VLOOKUP(value, table, column number, FALSE) for an exact match.
• XLOOKUP is a newer, more flexible lookup function, available in Microsoft 365 and Excel 2021 onwards. It can look left or right and gives an exact match by default.
• $A$1 is an absolute reference (does not change when copied); A1 is relative. F4 switches between the reference types.

Excel shortcuts and errors; PowerPoint

• Excel: Alt + = AutoSum; Ctrl + ; inserts today's date; Ctrl + Shift + : inserts the current time; F2 edits the active cell; Ctrl + 1 opens Format Cells.
• Excel errors: #DIV/0! (division by zero), #N/A (value not found), #NAME? (wrong function name), #REF! (invalid cell reference), ##### (column too narrow).
• PowerPoint is for presentations; its default extension is .pptx. Ctrl + M adds a new slide.
• F5 starts the slide show from the first slide; Shift + F5 starts from the current slide; Esc ends the show.
• A transition is the effect between two slides; an animation is the effect on an object (text or picture) within a slide.
• Slide Sorter view shows small versions of all slides so you can rearrange them.

💡 For Excel functions, remember the argument order: VLOOKUP(what to find, where to look, which column, FALSE). Exams often change one argument in the options.

📝 5-question quiz on this lesson: enrol free to take it and track your score.

4. Internet, Networking, Cyber Security and Digital India

SSC, Railway and Bank exams ask many easy questions on networks, the internet, online safety and government digital services. This lesson explains how networks and the internet work, how to protect yourself from online fraud, and the main Digital India services and laws. Learn the full forms well, because they are asked again and again.

Networks, the internet and protocols

• Types of network by size: LAN (Local Area Network) covers one room, building or campus; MAN (Metropolitan Area Network) covers a city; WAN (Wide Area Network) covers countries. The internet is the biggest WAN.
• Devices: a router joins different networks and sends data between them; a switch joins devices inside one LAN; a modem (modulator-demodulator) changes digital data into signals for a phone or cable line and back.
• Every device on a network has an IP (Internet Protocol) address. IPv4 addresses are 32 bits long; IPv6 addresses are 128 bits long. DNS (Domain Name System) changes a name like india.gov.in into an IP address.
• A URL (Uniform Resource Locator) is the address of a web page. HTTP carries web pages; HTTPS is the secure, encrypted form of HTTP and shows a padlock in the browser.
• Email protocols: SMTP sends email; POP3 and IMAP receive email. FTP (File Transfer Protocol) moves files. In an email, CC copies are seen by all; BCC copies are hidden from the other receivers.
• Wi-Fi is wireless networking based on the IEEE 802.11 standards. Bluetooth connects nearby devices over a short range. Chrome, Firefox, Edge and Safari are web browsers; Google and Bing are search engines.

Cyber security and safe use

• Phishing is a fake email or website that tries to steal passwords or bank details. Vishing is the same trick by voice call; smishing is by SMS.
• Malware means harmful software. A virus attaches itself to files; a worm spreads on its own over a network; a Trojan looks like useful software; ransomware locks your files and asks for money; spyware secretly watches what you do.
• A firewall blocks unwanted network traffic. Antivirus software finds and removes malware. Two-factor authentication (2FA) adds a second check, such as an OTP, after the password.
• Use long, strong passwords and a different password for each account. Never share OTP, PIN, CVV or UPI PIN with anyone, even if the caller says he is from a bank or the police.
• Report cyber fraud quickly: call the national helpline 1930 or complain online at cybercrime.gov.in (National Cyber Crime Reporting Portal, run by the Ministry of Home Affairs).
• CERT-In (Indian Computer Emergency Response Team) is the national agency for handling cyber security incidents. It works under MeitY (Ministry of Electronics and Information Technology).

Digital India: programme and services

• The Digital India programme was launched on 1 July 2015 by the Government of India. MeitY is the nodal ministry. Its aim is to make India a digitally empowered society and knowledge economy.
• Aadhaar is a 12-digit unique identity number issued by UIDAI (Unique Identification Authority of India). DigiLocker is a cloud wallet where citizens keep and share official documents such as marksheets and driving licences.
• UMANG (Unified Mobile Application for New-age Governance) is one mobile app for many central and state government services. CSCs (Common Service Centres) give digital services to people in villages through local operators.
• BharatNet aims to connect all gram panchayats with high-speed broadband using optical fibre. UPI (Unified Payments Interface) was launched in 2016 by NPCI (National Payments Corporation of India) for instant mobile payments.
• e-Sign lets a person sign a document online using Aadhaar-based authentication. GeM (Government e-Marketplace, 2016) is the online portal where government offices buy goods and services. MyGov (2014) is the citizen participation platform.
• CoWIN was used for COVID-19 vaccination. U-WIN, launched nationally on 29 October 2024, records routine vaccinations of pregnant women and children under the Universal Immunisation Programme.

Cyber laws and common full forms

• The Information Technology Act, 2000 (IT Act) is India's main cyber law. It gives legal recognition to electronic records and digital signatures and punishes cyber crimes. It was amended in 2008.
• The Digital Personal Data Protection Act, 2023 (DPDP Act) protects people's personal data. The person whose data is used is the Data Principal; the organisation that decides how to use it is the Data Fiduciary.
• The DPDP Rules were notified in November 2025, with obligations phased in over the following 12-18 months. The Data Protection Board of India handles complaints and can impose penalties of up to Rs 250 crore.
• Full forms: CPU Central Processing Unit; RAM Random Access Memory; ROM Read Only Memory; USB Universal Serial Bus; BIOS Basic Input/Output System; OS Operating System.
• Full forms: WWW World Wide Web; HTML HyperText Markup Language; ISP Internet Service Provider; VPN Virtual Private Network; OTP One Time Password; PDF Portable Document Format.

💡 Make a two-column table: service name on the left, what it does and who runs it on the right (for example, UPI - instant payments - NPCI). Revise it with the full forms list every day in the last week.

📝 5-question quiz on this lesson: enrol free to take it and track your score.