Computer Science
Fundamentals

Binary (Base 2) — Uses digits 0, 1. The language computers speak internally.
Octal (Base 8) — Uses digits 0–7. Each octal digit = 3 binary bits.
Decimal (Base 10) — Uses digits 0–9. The number system humans use daily.
Hexadecimal (Base 16) — Uses digits 0–9 and letters A–F. Each hex digit = 4 binary bits.

Binary → Decimal: Multiply each bit by 2 raised to its position (rightmost = 0).
  Example: 1011 = 1×8 + 0×4 + 1×2 + 1×1 = 11

Decimal → Binary: Divide by 2, collect remainders bottom-up.
  Example: 13 → 1101

Binary → Octal: Group bits in threes from the right.
  Example: 110 100 101 → 645

Binary → Hexadecimal: Group bits in fours from the right.
  Example: 1011 0101 → B5

Hex A=10, B=11, C=12, D=13, E=14, F=15

In signed binary, the leftmost (most significant) bit is the sign bit: 0 = positive, 1 = negative.
Example: 101 → sign bit is 1 (negative), remaining bits 01 = 1, so value is −1? No — in sign-magnitude: 101 = −(01) = −1... but check context: the question bank uses sign-magnitude where 101 = −1 in 3-bit or −2 depending on bit count. Always read sign bit first.

BCD (Binary Coded Decimal): Each decimal digit is encoded into 4 bits separately. E.g., 91 → 1001 0001.

Gen	Era	Technology	Example
1st	1940s–50s	Vacuum Tubes	ENIAC, UNIVAC
2nd	1950s–60s	Transistors	IBM 7090
3rd	1960s–70s	Integrated Circuits (ICs)	IBM 360
4th	1970s–present	VLSI Microprocessors	Intel PCs
5th	Present–future	AI / KIPS	AI systems

Microcomputer (PC) → Minicomputer → Mainframe → Supercomputer

• PDA — Personal Digital Assistant, uses handheld OS
• Supercomputer — hundreds of billions of instructions/sec; used for weather forecasting, scientific simulations
• Hybrid Computer — processes both analog and digital data

• ENIAC — first general-purpose electronic computer (designed by J. Presper Eckert & John Mauchly)
• EDVAC — Electronic Discrete Variable Automatic Computer
• Abacus — earliest calculating device
• Blaise Pascal — invented the adding machine
• Herman Hollerith — invented punched cards
• FORTRAN — introduced in 1957
• First microprocessor — developed by Intel in 1971
• First PC virus — developed in 1986
• Laptops — invented by Adam Osborne

Control Unit (CU) — Interprets instructions, directs all operations
Arithmetic Logic Unit (ALU) — Performs all math and logical operations
Registers — Ultra-fast, tiny storage inside the CPU (e.g., accumulator holds operation results)
Cache Memory — Fast buffer memory between CPU and RAM; stores frequently accessed data

The CPU is the brain of the computer. It reads, interprets, and processes instructions.

Memory	Volatile?	Purpose
RAM	✅ Yes (lost on power off)	Active program/data storage
ROM	❌ No (permanent)	BIOS, firmware; read-only
Cache	✅ Yes	Fast CPU buffer
EPROM	❌ No	Erasable programmable ROM
CMOS	Special	Stores BIOS settings; battery-backed

BIOS (Basic Input Output System) is stored in Flash Memory and runs the Power-On Self Test (POST) on boot.

Bit → Nibble (4 bits) → Byte (8 bits) → Kilobyte (~1,000 B) → Megabyte (~1 million B) → Gigabyte (~1 billion B) → Terabyte

• 1 MB = 1,048,576 bytes (exact) or ~1 million bytes
• A 6-bit word can represent max value 63 (2⁶−1)
• Nibble = half a byte = 4 bits = 16 possible values

Primary (Main) Memory: RAM, ROM — directly accessible by CPU, fast
Secondary Storage: HDD, SSD, Pen Drive, CD/DVD — persistent, non-volatile
Tertiary/Auxiliary: Magnetic tape — sequential access, used for backups

CD Types:
  • CD-ROM — read-only
  • CD-R — write once
  • CD-RW — rewritable (labeled RW)
Max CD capacity: ~700–750 MB
CD-ROM life span: ~25 years

Access methods: Sequential (magnetic tape) vs. Random (HDD, SSD)

USB (Universal Serial Bus) — Flash drives, peripherals
FireWire — Digital camcorder interfacing, high-speed video transfer
SMPS (Switch Mode Power Supply) — converts AC to DC for computer components
Hot Swapping — removing/replacing devices without turning off the computer

LAN (Local Area Network) — small, single-site; multi-user; hub connects star topology
WAN (Wide Area Network) — geographically distributed; connects office LANs
MAN — Metropolitan Area Network (city-wide)

Topologies: Bus, Star, Ring, Mesh (most reliable = Mesh)

#	Layer	Key Function
7	Application	User interface (HTTP, FTP)
6	Presentation	Encryption, decryption, data format
5	Session	Dialogue control, token management
4	Transport	End-to-end delivery, TCP/UDP
3	Network	Routing (Router operates here)
2	Data Link	Framing, MAC address (Bridge/Switch)
1	Physical	Bits over medium (Repeater)

Hub — connects devices in a star network; broadcasts to all
Switch — smarter than hub; sends data to specific device
Router — forwards packets between networks; IP layer
Repeater — extends network range by amplifying signal (Physical layer)
Bridge — connects two LAN segments (Data Link layer)
Modem — converts digital↔analog for telephone lines; DSL is broadband
Firewall — protects against unauthorized intrusions

TCP/IP — standard protocol of the Internet
HTTP (port 80) — web page linking/transfer
SMTP — email sending (relay agent)
FTP — file transfer
DNS — converts domain names to IP addresses
TELNET — remote login
SNMP — network management
URL — used by browser to connect to internet resources

WWW — World Wide Web
Web Browser — software to surf the internet (Chrome, Firefox, IE, not Twitter)
URL — Unique address of a website
Home Page — first page that appears when opening a website
Hyperlink — clickable word/image that opens another document
Search Engine — Google, Bing (locates web pages)
Metasearch Engine — searches multiple engines simultaneously
Streaming — media plays as it downloads

Email address format: username@domain.com
Subject — describes message contents
CC — Carbon Copy; BCC — Blind Carbon Copy
Attachment — separate document sent with email
Spam — junk email
Draft folder — saves unsent/unfinished emails
Inbox — received mail; Outbox — being sent
Thunderbird — example email program (not MS-Word or IE)

B2C — Business to Consumer (direct retail)
m-commerce — transactions over mobile phone
E-Governance — citizens accessing government services online
Electronic Funds Transfer — money transfer between accounts electronically

The OS is system software — a layer between hardware and user programs that:
• Controls internal operations and hardware
• Manages files, memory, processes
• Creates virtual computers from physical hardware

Examples: Windows, Linux (Open Source), UNIX (multi-user), DOS (single-user), macOS
NOT an OS: DBMS, MS-Access, MS-Word

Booting = starting/loading the operating system into memory
POST (Power-On Self Test) — runs first to check all components
Cold boot — starting from off; uses system disk
Warm boot — restart while on (e.g., standby mode wakes with key press)
BIOS stored in Flash Memory — initiates boot sequence

Root Directory — main/top-level folder on a storage device
File extension — identifies the file type (e.g., .docx, .xlsx, .accdb)
Recycle Bin — deleted files go here
My Documents — personal files storage
Save As — save existing file with new name/location

MS Access extension: .accdb or .mdb
MS Word default: .doc

Multitasking — OS runs more than one application simultaneously
Multiprocessing — multiple CPUs process simultaneously
Multiprogramming — multiple programs in memory at once
Swapping — moving process from main memory to disk
Spooling — queuing output (e.g., print jobs) for processing
Batch Processing — accumulates and processes a large set together

Ctrl+A — Select all  |  Ctrl+Enter — Page break
Ctrl+H — Find & Replace  |  Tab — Indent paragraph
Home key — move to beginning of line
Backspace — delete left  |  Delete — delete right
Alt+F4 — close Word
Thesaurus — find alternative words
Status bar — shows page number, word count
Cut and Paste — most efficient way to move paragraphs
Default line spacing: 1.15 | Default print mode: Portrait

Cell address — column letter + row number (e.g., E12 = Column E, Row 12)
Active cell — indicated by dark wide border
Formula bar — shows active cell contents
Name box — appears left of formula bar; shows cell location
Workbook — contains one or more worksheets
Sheet tab — click to move between worksheets
AutoFill — extends sequential data series
COUNTIF — count cells based on condition
Ctrl+; — insert current date
Ctrl+K — insert hyperlink
Pivot Table — found in Insert tab
Chart Wizard — used to create charts
$A$1 — absolute cell reference

Ctrl+M — insert new slide
Ctrl+1 + Enter — return to first slide during slideshow
Normal View — primary editing view
Animations — visual/sound effects in presentation
Design Template — provides fonts, colors, concept
Header & Footer — Insert menu → slide tab → Apply to All

Machine Language (1GL) — binary code; directly understood by CPU
Assembly Language (2GL) — mnemonics; needs assembler
High-Level Language (3GL) — English-like; needs compiler/interpreter
  Examples: C, C++, Java, BASIC, COBOL, FORTRAN, PASCAL

Source code — program written in high-level language
Object code — machine language output from compiler

Compiler — translates entire program into machine code at once → creates executable
Interpreter — translates and executes line by line (e.g., BASIC)
Assembler — translates assembly language to machine code
Java — uses both compiler (to bytecode) and interpreter (JVM)
Visual Basic — interpreted

C — Dennis M. Ritchie
C++ — Bjarne Stroustrup (Object-Oriented)
PASCAL — Niklaus Wirth (named after Blaise Pascal)
PROLOG — associated with Artificial Intelligence
FORTRAN — first scientific language (1957)
COBOL — business processing
Java — web/multimedia development (James Gosling)

Virus — destroys data; travels to infect other computers
VIRUS stands for: Vital Information Resource Under Siege
Spyware / Malware — malicious software (Hub is NOT malware — it's a network device)
Phishing — fraudulent emails stealing info; Smishing — same via SMS
Pharming — redirects to fake website

Firewall — protects against hacker intrusions
Encryption — alters data so it's unreadable without decryption key (Presentation layer in OSI)
Hamming Codes — detect and correct errors in data
Password — coded entry to gain access
Backup — copying data to a different destination to prevent loss
RFID tags — used to track animal movements in databases

AI — science that produces machines displaying human-like intelligence
Father of AI — John McCarthy
PROLOG — programming language associated with AI
5th Generation — based on AI / Knowledge Information Processing Systems (KIPS)
Robotics — surgeons use computers to manipulate devices remotely
Nanotechnology — building devices at molecular scale (1–100 nanometers)

Database — collection of interrelated records
DBMS — Database Management System; manages data in multiple files
Tuple — a row of a table
Field — identified by field name
Primary Key — uniquely identifies a record
Data hierarchy: Character → Field → Record → File → Database
DFD — Data Flow Diagram
CRM — Customer Relationship Management
Data mining — studying buying patterns to support business decisions

Input Devices: Keyboard, Mouse, Scanner, Microphone, OCR, Digital Camera, Joystick, Light Pen, Touch Tablet
Output Devices: Monitor, Speaker, Printer, Plotter
Both (I/O): Modem, Touch Screen

Mouse — pointing + input device
Cursor — blinking screen symbol showing next character placement
Pixel — smallest resolvable part of a picture
MP3 — sound/audio format

Abbreviation	Full Form
GUI	Graphical User Interface
PDF	Portable Document Format
ASCII	American Standard Code for Information Interchange (7-bit)
BIOS	Basic Input Output System
OCR	Optical Character Recognition
CMOS	Complementary Metal Oxide Semiconductor
DMA	Direct Memory Access
USB	Universal Serial Bus
LSI	Large-Scale Integration
SIM	Subscriber Identity Module
IDE	Integrated Development Environment
ADSL	Asymmetric Digital Subscriber Line
RPC	Remote Procedure Call
CMS	Content Management System
UTP	Unshielded Twisted Pair
IBM	International Business Machines