SSC Computer Knowledge — Complete Study Notes

Topics Covered

1. Computer Basics 2. Hardware 3. Software 4. Operating System 5. Memory & Storage 6. Networking 7. Internet 8. MS Office 9. Keyboard Shortcuts 10. Cybersecurity 11. Database Basics 12. Computer Generations

Computer Basics

Definition & Characteristics

A computer is an electronic machine that accepts data (input), processes it, and gives useful information (output), and stores data for future use.

Characteristics: Speed, Accuracy, Diligence (no fatigue), Versatility, Storage
Father of computer: Charles Babbage (Analytical Engine)
First electronic computer: ENIAC (1945, USA)
First computer in India: HEC-2M (1956, ISI Calcutta)

Number Systems

System	Base	Digits Used	Example
Binary	2	0, 1	1010 = 10 decimal
Octal	8	0–7	12 = 10 decimal
Decimal	10	0–9	10 = 10 decimal
Hexadecimal	16	0–9, A–F	A = 10, F = 15

Binary Conversions

1 Bit = smallest unit (0 or 1)
1 Nibble = 4 bits
1 Byte = 8 bits
1 KB = 1024 Bytes = 2¹⁰ bytes
1 MB = 1024 KB = 2²⁰ bytes
1 GB = 1024 MB = 2³⁰ bytes
1 TB = 1024 GB = 2⁴⁰ bytes
1 PB = 1024 TB
ASCII: American Standard Code for Info Interchange (7-bit, 128 characters)
Unicode: 16-bit code; supports all world languages

Hardware

Input Devices

Common Input Devices

Keyboard, Mouse (pointing device), Scanner, Microphone, Webcam, Joystick, Light Pen, Touch Screen, Trackball, Barcode Reader, OCR (Optical Character Reader), MICR (Magnetic Ink Character Recognition — used in bank cheques), OMR (Optical Mark Recognition — used in answer sheets)

Output Devices

Common Output Devices

Monitor/VDU (Visual Display Unit), Printer, Speaker, Plotter (for large technical drawings), Projector

Printer types:
Impact: Dot Matrix, Daisy Wheel (use ribbon/physical impact)
Non-impact: Inkjet (sprays ink), Laser (uses toner powder — fastest, best quality), Thermal (uses heat — ATM receipts)

CPU (Central Processing Unit)

CPU Components

ALU (Arithmetic Logic Unit): Arithmetic (+, −, ×, ÷) and logical (AND, OR, NOT) operations
CU (Control Unit): Directs and coordinates all computer operations; fetches, decodes, and executes instructions
Registers: Very fast, small storage within CPU (PC, IR, MAR, MDR, Accumulator)
Cache memory: Between CPU and RAM; fastest memory; L1 (fastest, smallest), L2, L3

Clock speed: Measured in GHz; higher = faster processor (e.g., 3.5 GHz = 3.5 billion cycles/sec)

Software

Types of Software

Type	Description	Examples
System Software	Manages hardware and provides platform for other software	OS (Windows, Linux), Device drivers, BIOS
Application Software	Specific user tasks	MS Office, Photoshop, browsers, games
Utility Software	Maintenance and support	Antivirus, Disk cleanup, File compressors (WinRAR, 7-Zip)
Programming Software	Create other programs	Compilers, Interpreters, IDEs (VS Code)

Programming Languages

Language	Level	Use / Note
Machine language	Lowest (binary)	Directly understood by CPU; 0s and 1s
Assembly language	Low level	Uses mnemonics (MOV, ADD); translated by assembler
FORTRAN	High level	First high-level language; scientific computing
COBOL	High level	Business applications
C, C++	High level	System programming, general purpose
Java	High level	Platform independent; "Write once run anywhere"
Python	High level	AI/ML, data science; readable syntax
HTML	Markup	Web pages; not a programming language

💡 Compiler vs Interpreter

Compiler: Translates entire program at once → faster execution (C, C++, Java)
Interpreter: Translates line by line → slower but easier debugging (Python, JavaScript)

Operating System

What is OS?

System software that manages hardware and software resources. It is the interface between user and hardware.

Functions: Process management, Memory management, File management, Device management, User interface

Types of Operating Systems

Type	Description	Example
Batch OS	Jobs processed in groups (no user interaction)	Early mainframe systems
Time-sharing OS	Multiple users share CPU time	Unix
Real-time OS (RTOS)	Processes data with minimal delay	Embedded systems, robots
Distributed OS	Multiple computers as one	Network OS
Multitasking OS	Runs multiple programs simultaneously	Windows, macOS, Linux
Multi-user OS	Supports multiple users at once	Unix, Linux

Popular Operating Systems

OS Examples & Developers

Windows: Microsoft | macOS: Apple | Linux: Linus Torvalds (1991); open-source
Android: Google (Linux-based) | iOS: Apple
MS-DOS: first OS for PCs (Microsoft, 1981) — single-user, command line
UNIX: AT&T Bell Labs (1969) | Free BSD, Red Hat, Ubuntu, Fedora (Linux distributions)

Memory & Storage

Primary Memory (Internal)

Type	Full Form	Nature	Speed / Use
RAM	Random Access Memory	Volatile (lost on power off)	Main working memory; temporary
ROM	Read Only Memory	Non-volatile (permanent)	BIOS stored; cannot be modified
PROM	Programmable ROM	Non-volatile	Written once
EPROM	Erasable PROM	Non-volatile	Erased by UV light
EEPROM	Electrically Erasable PROM	Non-volatile	Flash memory based
Cache	—	Volatile	Fastest; between CPU and RAM

💡 RAM Types

SRAM (Static RAM): Faster, costlier, used as cache | DRAM (Dynamic RAM): Slower, cheaper, used as main RAM
DDR4, DDR5: Modern RAM standards in laptops/PCs

Secondary Storage (External)

Storage Device	Type	Key Facts
HDD (Hard Disk Drive)	Magnetic	Rotating platters; large capacity; slower; 5400–7200 RPM
SSD (Solid State Drive)	Flash/Electronic	Faster, no moving parts; expensive; increasing use
CD (Compact Disc)	Optical	650–700 MB capacity; 12 cm disc
DVD (Digital Versatile Disc)	Optical	4.7 GB (single layer) to 8.5 GB (dual layer)
Blu-ray	Optical	25 GB (single layer); blue laser
USB Flash Drive	Flash	Portable; plug & play
Memory Card	Flash	SD card, MicroSD (cameras, phones)
Magnetic Tape	Magnetic	Sequential access; backup use

Networking

Types of Networks

Network	Full Form	Range	Example
PAN	Personal Area Network	~10 m	Bluetooth, USB
LAN	Local Area Network	Building/campus	Office network, Ethernet
MAN	Metropolitan Area Network	City-wide	Cable TV network
WAN	Wide Area Network	Country/globe	Internet

Network Topologies

Topology Types

Bus: All devices on a single cable; simple but single point of failure
Star: All devices connect to central hub/switch; most common; hub failure = network down
Ring: Devices in a circle; data travels in one direction; token passing
Mesh: Every device connected to every other; most reliable; costly
Tree (Hierarchical): Star networks connected in a tree structure

Network Devices

Device	Layer	Function
Hub	Physical (Layer 1)	Broadcasts data to all devices; dumb
Switch	Data Link (Layer 2)	Sends data to specific device (MAC address); intelligent
Router	Network (Layer 3)	Routes data between different networks (IP address)
Modem	Physical	Modulates/demodulates signals (digital ↔ analog)
NIC	Data Link	Network Interface Card; connects device to network
Repeater	Physical	Amplifies/regenerates signal over long distances
Bridge	Data Link	Connects two similar networks
Gateway	All layers	Connects networks with different protocols

Network Protocols

Important Protocols

TCP/IP: Foundation of internet; TCP = reliable delivery; IP = addressing
HTTP: HyperText Transfer Protocol — web browsing (port 80)
HTTPS: HTTP Secure — encrypted (port 443) using SSL/TLS
FTP: File Transfer Protocol — transfer files (port 21)
SMTP: Simple Mail Transfer Protocol — send emails (port 25)
POP3: Post Office Protocol — receive emails (port 110)
IMAP: Internet Message Access Protocol — receive emails (port 143)
DNS: Domain Name System — converts domain names to IP addresses
DHCP: Dynamic Host Configuration Protocol — automatically assigns IP addresses
IP Address: Unique 32-bit address (IPv4: 192.168.1.1); IPv6 = 128-bit
MAC Address: 48-bit hardware address (e.g. 00:1A:2B:3C:4D:5E)

Internet

Internet Basics

Key Facts

Internet: Global network of networks connected via TCP/IP
Tim Berners-Lee: Invented World Wide Web (WWW) in 1989 at CERN
ARPANET (1969): Predecessor to internet (US Defense)
India's first internet service: 1995 (VSNL — Videsh Sanchar Nigam Limited)

Browser: Software to access web (Chrome, Firefox, Safari, Edge)
Search Engine: Finds web pages (Google, Bing, Yahoo, DuckDuckGo)
ISP: Internet Service Provider (BSNL, Airtel, Jio — in India)

Internet Terminology

Term	Meaning
URL	Uniform Resource Locator — web address (e.g. https://www.google.com)
IP Address	Unique numeric address of each device on internet
Domain Name	Human-readable web address (google.com)
ISP	Internet Service Provider
WWW	World Wide Web — system of interlinked documents (HTML pages)
Email	Electronic mail; format: user@domain.com
Blog	Web log — personal/informational website
Download	Transfer data FROM internet TO computer
Upload	Transfer data FROM computer TO internet
Bandwidth	Data transfer capacity (Mbps — megabits per second)
Cookie	Small data stored on browser by websites (remember preferences)
Cache	Temporary storage of web pages for faster loading
VPN	Virtual Private Network — encrypted connection

MS Office

MS Word (Word Processor)

Key Points

File extension: .docx (Word 2007+) | .doc (older versions)
Default margins: 1 inch on all sides
Default font: Calibri (11pt) in Word 2013+
Mail Merge: Merge a template letter with data from Excel/database
Autocorrect: Automatically fixes common typos
Track Changes: Monitors all edits made to document
Ruler: Shows margins and tab stops
Non-printing characters (¶): Para marks, spaces visible with Ctrl+Shift+8

MS Excel (Spreadsheet)

Key Points

File extension: .xlsx | Default: 1,048,576 rows × 16,384 columns (XFD)
Cell address: Column letter + Row number (e.g. A1, B5, $A$1 = absolute)
Formula: Always starts with = (e.g. =SUM(A1:A10), =AVERAGE(B1:B5))
Functions: SUM, AVERAGE, MAX, MIN, COUNT, IF, VLOOKUP, HLOOKUP
VLOOKUP: =VLOOKUP(lookup_value, table_array, col_index, [range_lookup])
Pie chart: Shows proportion | Bar chart: Comparison | Line chart: Trends
Pivot Table: Summarises large datasets; dynamic analysis

MS PowerPoint (Presentation)

Key Points

File extension: .pptx | Presentation = collection of slides
Default slide layout: Blank, Title Slide, Title and Content
Slide Transition: Animation between slides
Animation: Effect on individual objects within a slide
Slide Show: F5 (from beginning) | Shift+F5 (from current slide)
Master Slide: Changes apply to all slides using that layout
Handout: Printout of slides (3 slides per page has writing lines)

MS Access (Database)

Key Points

File extension: .accdb
Objects: Tables (store data), Queries (retrieve/filter data), Forms (user input), Reports (formatted output)
Primary Key: Uniquely identifies each record in a table
Foreign Key: Links one table to another
SQL (Structured Query Language): Used to manage databases
SELECT * FROM TableName WHERE condition;
RDBMS: Relational Database Management System (Oracle, MySQL, SQL Server, PostgreSQL)

Keyboard Shortcuts (Windows)

General Windows Shortcuts

Ctrl + C

Copy selected item

Ctrl + X

Cut selected item

Ctrl + V

Paste

Ctrl + Z

Undo last action

Ctrl + Y

Redo

Ctrl + A

Select all

Ctrl + S

Save

Ctrl + P

Ctrl + F

Find

Ctrl + H

Find and Replace

Alt + F4

Close current window/program

Alt + Tab

Switch between open windows

Win + D

Show/hide desktop

Win + E

Open File Explorer

Win + R

Open Run dialog

Help in most programs

Refresh (browser/explorer)

Delete

Delete to Recycle Bin

Shift + Delete

Permanently delete (no Recycle Bin)

Print Screen

Screenshot to clipboard

MS Word / Excel Shortcuts

Ctrl + B

Bold

Ctrl + I

Italic

Ctrl + U

Underline

Ctrl + K

Insert Hyperlink

Ctrl + E

Center align

Ctrl + L

Left align

Ctrl + R

Right align

Ctrl + J

Justify text

Ctrl + Home

Go to beginning of document

Ctrl + End

Go to end of document

Ctrl + Enter

Page break (Word) / new cell (Excel)

Spell check

Cybersecurity

Types of Malware

Malware Type	Description
Virus	Self-replicating program that attaches to files; spreads when files shared
Worm	Self-replicates and spreads via network WITHOUT human action
Trojan Horse	Disguised as legitimate software; does not self-replicate
Ransomware	Encrypts victim's files; demands ransom for decryption key
Spyware	Secretly monitors user activity; steals data
Adware	Displays unwanted advertisements
Keylogger	Records keystrokes; steals passwords
Rootkit	Hides malicious software; gives admin control to attacker
Botnet	Network of infected computers controlled remotely

Types of Cyber Attacks

Common Attacks

Phishing: Fake emails/websites to steal credentials; most common social engineering attack
Man-in-the-Middle (MitM): Attacker intercepts communication between two parties
DoS/DDoS: Denial of Service / Distributed DoS — floods server with traffic to crash it
SQL Injection: Malicious SQL code in input fields to access/modify database
Cross-Site Scripting (XSS): Injects malicious scripts into websites
Brute Force: Trying all possible passwords until correct one is found
Social Engineering: Manipulates humans to reveal confidential information

Security Measures

✓ Protection Methods

Firewall: Network security system that monitors and controls incoming/outgoing traffic based on rules
Antivirus: Detects and removes malware
Encryption: Converting data into unreadable format (SSL/TLS for websites)
Two-Factor Authentication (2FA): Password + second factor (OTP, biometric)
VPN: Encrypts all internet traffic; hides IP address
Digital Signature: Verifies authenticity and integrity of digital documents
Biometrics: Authentication using fingerprint, face, iris, voice

Database Basics

SQL Basics

SELECT: Retrieve data → SELECT * FROM Students;
INSERT: Add new data → INSERT INTO Students VALUES (1, 'Rahul', 20);
UPDATE: Modify data → UPDATE Students SET Age=21 WHERE ID=1;
DELETE: Remove data → DELETE FROM Students WHERE ID=1;
CREATE TABLE: Define new table structure
DROP TABLE: Delete entire table
WHERE: Filter condition | ORDER BY: Sort | GROUP BY: Group records
JOIN: Combine rows from multiple tables (INNER, LEFT, RIGHT, FULL)

Database Concepts

DBMS: Database Management System — software to manage databases
RDBMS: Relational DBMS — data in tables (rows & columns); MySQL, Oracle, PostgreSQL
Primary Key: Unique identifier for each row; cannot be NULL
Foreign Key: References primary key of another table
Normalization: Organizing data to reduce redundancy
ACID properties: Atomicity, Consistency, Isolation, Durability (for reliable transactions)
NoSQL: Non-relational database; MongoDB (document), Redis (key-value), Cassandra (wide-column)

Computer Generations

Generation	Period	Technology	Examples
1st	1940s–1950s	Vacuum tubes	ENIAC, UNIVAC I
2nd	1950s–1960s	Transistors	IBM 1401, CDC 1604
3rd	1960s–1970s	Integrated Circuits (ICs)	IBM 360, PDP-8
4th	1970s–1980s	Microprocessors (VLSI)	Intel 4004, IBM PC, Apple II
5th	1980s–present	AI, Parallel processing, ULSI	Modern AI systems

Classification by Size

Supercomputer: Most powerful; scientific research (India's PARAM series)
Mainframe: Large, multi-user; banking/government
Minicomputer: Medium; DEC PDP series
Workstation: Powerful desktop; engineering/graphics
Personal Computer (PC): Desktop, Laptop, Notebook, Tablet
Embedded Computer: Inside devices (microwave, car, ATM)

India's fastest supercomputer: PARAM Pravega (IISc Bengaluru)