Components of a Computer – Complete Guide for JKSSB / JKPSC / Police Exams

Computer Notes · JKSSB / JKPSC / FAA / Police SI / Junior Assistant

Components of a Computer — Complete Guide
All PYQs & New Pattern MCQs

CPU · ALU · CU · RAM · ROM · Input/Output · Storage · Motherboard · Number Systems · Bus System

📌 About This Post

This is the corrected and fully upgraded version of the Components of a Computer guide. It covers every component asked in JKSSB, JKPSC, FAA, Police SI, Junior Assistant and all J&K competitive exams — with complete theory, comparison tables, all PYQs and new statement-based pattern MCQs. This is the most comprehensive version of this topic on JKEdusphere.

// Contents

1. Overview 2. Input Unit 3. CPU 4. Memory 5. Output Unit 6. Storage 7. Motherboard 8. Number Systems 9. Bus System 10. All PYQs 11. New Pattern MCQs

1. Overview — The Five Functional Units

A computer system is made up of five fundamental functional units that work together to process data. Every computer — from a smartphone to a supercomputer — has all five of these units.

⌨️

INPUT UNIT

Keyboard, Mouse

🧠

CPU

ALU + CU + Registers

💾

MEMORY UNIT

RAM, ROM, Cache

🖥️

OUTPUT UNIT

Monitor, Printer

💿

STORAGE UNIT

HDD, SSD, USB

Functional Unit	Role	Examples
Input Unit	Accepts data and instructions from the user or external source and converts them into binary form for the CPU to process.	Keyboard, Mouse, Scanner, Microphone, Webcam, Joystick, OMR, OCR, MICR
Central Processing Unit (CPU)	The brain — executes instructions. Contains ALU (calculations), CU (control), and Registers (fastest memory). Also called processor.	Intel Core i7, AMD Ryzen 5, Apple M2
Memory Unit	Stores data and instructions — Primary (RAM, ROM, Cache) for current operations, Secondary for permanent storage.	RAM, ROM, Cache, HDD, SSD, USB
Output Unit	Presents processed results to the user in human-readable form — visual, audio or printed.	Monitor, Printer, Speaker, Projector, Plotter
Storage Unit	Non-volatile secondary storage — retains data permanently even without power.	HDD, SSD, DVD, Blu-ray, USB Flash Drive, Cloud

🎯 JKSSB Key Fact: The basic operation cycle of a computer is the IPO Cycle — Input → Process → Output. Storage is sometimes added making it IPSO. The CPU is called the 'Brain of the Computer'. John von Neumann's architecture (stored program concept) is the basis of all modern computers.

2. Input Unit — All Input Devices

The Input Unit is responsible for accepting raw data and instructions from the outside world and converting them into binary (machine-readable) form. Without input devices, a user cannot communicate with the computer.

Input Device	Key Facts	Exam Status
Keyboard	Most common input device. Standard layout has 104 keys (US layout). Invented by Christopher Latham Sholes (1868). Layouts: QWERTY, DVORAK, AZERTY. Types: Mechanical, Membrane, Virtual.	JKSSB PYQ ⭐
Mouse	Pointing device — controls cursor. Invented by Douglas Engelbart (1963). Types: Mechanical (ball), Optical (LED), Laser, Wireless. Standard mouse has 2 buttons + scroll wheel.	JKSSB PYQ ⭐
Scanner	Converts physical documents/images into digital form. Types: Flatbed (most common), Handheld, Drum, Sheet-fed.	Common PYQ
Touchpad	Built into laptops — pressure-sensitive pad. Replaces mouse. Also called Trackpad.	FAA PYQ
Trackball	Stationary pointing device — ball on top rotated by thumb. Does not need to be moved across surface.	Asked in PYQs
Joystick	Pointing device with a stick that moves in all directions. Used in gaming and aircraft simulators. Has a ball at both upper and lower ends.	JKSSB PYQ ⭐
Light Pen	Pen-shaped device used to draw directly on a monitor screen. Detects light from screen pixels.	Direct screen input
Touch Screen	Input AND output device (both). Accepts input via finger or stylus. Types: Resistive (any touch), Capacitive (conductive touch — finger).	JKSSB PYQ ⭐ — I/O
Microphone	Converts sound waves into digital audio signals for input.	Audio input
Webcam	Captures real-time video/images for input. Used in video conferencing.	Video input
Digitizer / Graphics Tablet	Flat pad with stylus — used by designers and artists. Converts drawings to digital.	CAD/Design
OMR	Optical Mark Recognition — reads pen/pencil marks in predefined positions. Used for MCQ answer sheets. CANNOT read handwriting.	JKSSB Most Asked ⭐⭐
OCR	Optical Character Recognition — reads printed/handwritten text and converts to editable digital format.	JKSSB PYQ ⭐
MICR	Magnetic Ink Character Recognition — reads characters printed with magnetic ink. Used exclusively in banking for cheque processing.	JKSSB PYQ ⭐⭐
Barcode Reader	Uses laser to read barcodes (1D) on products. Used in supermarkets, inventory management.	PYQ
QR Code Reader	Camera-based reader for 2D QR codes. Used in payments, URLs. Stores more data than barcode.	Modern

🎯 Critical Input Device Facts:
• OMR = only reads MARKS (circles) — answer sheets. Cannot read handwriting
• OCR = reads TEXT and converts to editable format
• MICR = reads MAGNETIC INK — only in banking/cheques
• Touch Screen = BOTH Input AND Output device
• Keyboard = 104 keys (standard US), invented 1868
• Mouse = invented by Douglas Engelbart, 1963
• Trackball = stationary; Trackpad = laptop built-in

3. Central Processing Unit (CPU)

The CPU (Central Processing Unit) is the primary component that executes all instructions and processes all data. It is the brain of the computer. Every calculation, logical operation and data movement passes through the CPU.

The CPU has three main internal components:

CPU — CENTRAL PROCESSING UNIT

ALU — Arithmetic Logic Unit

Performs all arithmetic operations (addition, subtraction, multiplication, division) and logical operations (AND, OR, NOT, comparisons like >, <, =). This is the actual computation engine — the part that does the maths.

CU — Control Unit

Acts as the traffic controller of the CPU. Fetches instructions from memory, decodes them, and directs all other components to carry them out. Does NOT perform any calculations itself — only controls and coordinates.

Registers

Fastest and smallest memory — located inside the CPU chip itself. Temporarily holds the data and instructions currently being processed. Key registers: Accumulator, Program Counter (PC), Instruction Register (IR), Memory Address Register (MAR), Memory Buffer Register (MBR).

CPU — Key Specifications

Specification	Description	Exam Status
Clock Speed	Number of instruction cycles per second. Measured in GHz (Gigahertz). Higher GHz = faster CPU. Modern CPUs: 2–5 GHz.	JKSSB PYQ ⭐
Cores	Number of independent processing units in one chip. Dual Core (2), Quad Core (4), Hexa Core (6), Octa Core (8). More cores = better multitasking.	JKSSB PYQ ⭐
Cache Memory	Ultra-fast memory built into CPU chip. L1 (fastest, smallest — inside core), L2 (per core or shared), L3 (slowest, shared between all cores — largest).	Important
MIPS	Million Instructions Per Second — measures CPU performance/speed.	Exam term
FLOPS	Floating Point Operations Per Second — for scientific supercomputer performance.	Advanced
Word Size	Number of bits processed at once — 32-bit or 64-bit. 64-bit CPUs process more data per cycle and can access more RAM.	JKSSB PYQ
Thermal Design Power (TDP)	Heat generated by CPU — affects cooling requirements.	Background

Fetch-Decode-Execute Cycle (Machine Cycle)

1. FETCH

CU gets instruction from RAM

→

2. DECODE

CU interprets the instruction

→

3. EXECUTE

ALU/CU carries it out

→

4. STORE

Result saved to memory

CPU Manufacturers

Manufacturer	Products	Note
Intel	World's largest CPU maker. Core i3/i5/i7/i9 (consumer), Xeon (server), Celeron/Pentium (budget).	Most recognized brand
AMD	Intel's main rival. Ryzen 3/5/7/9 (consumer), EPYC (server), Athlon (budget).	Strong competitor
ARM	Designs CPU architectures — licensed to manufacturers. Used in all smartphones.	Apple M1/M2, Snapdragon, Exynos
Apple	Designs own ARM-based chips for Mac, iPhone, iPad. M1, M2, M3, A-series.	MacBook, iPhone
Qualcomm	Snapdragon series — dominates Android smartphones.	Mobile processors

🎯 CPU PYQ Facts — Most Asked:
• CPU = ALU + Control Unit + Registers
• ALU = does arithmetic AND logical operations
• Control Unit = controls/coordinates — does NOT calculate
• Registers = FASTEST memory — inside CPU
• Speed in GHz | Performance in MIPS
• Dual Core = 2, Quad = 4, Octa = 8 cores
• Intel and AMD = main CPU manufacturers for PCs

4. Memory Unit — Primary, Cache & Virtual Memory

Memory stores data and instructions for the CPU to use. Computer memory is classified into Primary Memory (directly accessible by CPU) and Secondary Memory (storage devices). Cache memory bridges the gap between CPU speed and RAM speed.

Memory Hierarchy

Speed ↑ Cost ↑ Size ↓  |  Fastest & Most Expensive at Top

CPU Registers

Inside CPU — data currently being processed

Fastest (~ps)

L1 Cache

Inside CPU core — 32KB–512KB per core

~1 ns

L2 Cache

Inside CPU — 256KB–8MB per core

~4 ns

L3 Cache

Shared between all cores — 8MB–64MB

~10 ns

RAM

Main working memory — programs run here — volatile

~100 ns

SSD

Flash storage — permanent, fast

~0.1 ms

HDD

Magnetic disk — permanent, slower

~5–10 ms

Optical/USB/Tape

CD/DVD, USB, magnetic tape — slowest

Slowest

RAM vs ROM — Most Asked Comparison

Type	Full Name	Volatility	Description	Used In
RAM	Random Access Memory	Volatile — data LOST when power off	CPU reads/writes data here during active programs. More RAM = better multitasking. Types: DRAM (main RAM), SRAM (Cache).	DDR4, DDR5 — 8GB, 16GB, 32GB typical
ROM	Read-Only Memory	Non-volatile — data RETAINED without power	Stores BIOS/firmware. Cannot be easily modified by programs. Contains startup instructions.	BIOS chip on motherboard
PROM	Programmable ROM	Non-volatile	Written ONCE after manufacture — cannot be erased.	One-time programmable devices
EPROM	Erasable Programmable ROM	Non-volatile	Erased using ultraviolet (UV) light and reprogrammed.	Older firmware chips
EEPROM	Electrically Erasable Programmable ROM	Non-volatile	Erased using electric current (no UV needed). Basis of Flash Memory.	USB drives, SSD, UEFI BIOS chips
DRAM	Dynamic RAM	Volatile	Needs refreshing thousands of times per second. Cheaper — used as main system RAM.	Main RAM in computers
SRAM	Static RAM	Volatile	No refreshing needed — faster but expensive. Used for Cache memory.	L1/L2/L3 Cache inside CPU

Virtual Memory

Virtual Memory is a memory management technique that uses a portion of the hard disk as an extension of RAM. When RAM is full, the OS moves less-used pages to the hard disk (swap space). This allows programs larger than physical RAM to run, but is much slower than real RAM.

Virtual Memory Term	Description
Pagefile.sys	Windows virtual memory file — stored on hard disk. Location: C:\pagefile.sys
Swap Partition / Swap File	Linux virtual memory — either a dedicated disk partition or a file
Thrashing	System slows severely when it spends more time swapping pages than executing processes — too many programs competing for limited RAM
Paging	Process of moving pages between RAM and virtual memory (hard disk)

🎯 Memory PYQ Facts — Most Asked:
• RAM = Volatile (data lost at shutdown) | ROM = Non-volatile
• SRAM = Cache (faster) | DRAM = main RAM (cheaper)
• EPROM erased by UV light | EEPROM erased by electricity
• 1 KB = 1024 Bytes (binary, NOT 1000)
• Virtual memory file in Windows = pagefile.sys
• Thrashing = system too slow due to excessive paging
• Registers = fastest memory; HDD = slowest

5. Output Unit — All Output Devices

The Output Unit receives processed data from the CPU and presents it to the user in human-readable form — visual, audio or printed.

Output Device	Key Facts	Exam Status
Monitor (VDU)	Primary visual output. VDU = Visual Display Unit. Screen size measured diagonally in inches. Resolution in pixels (1920×1080 = Full HD). Types: CRT (old, electron gun), LCD (liquid crystals, backlight), LED (LCD with LED backlight), OLED (self-illuminating pixels — no backlight), TFT (improved LCD).	JKSSB PYQ ⭐⭐
Printer	Produces hard copy (paper) output. Two types: Impact (physical contact with paper) and Non-Impact (no contact). Impact: Dot Matrix (pins+ribbon, cheapest, can do carbon copies), Daisy Wheel (high quality text, NO graphics), Line Printer (one line at a time, very fast), Drum Printer Non-Impact: Inkjet (sprays ink droplets, good for photos), Laser (fastest, best quality, uses toner powder), Thermal (heat on special paper, used in ATMs — no ink needed)	JKSSB Most Asked ⭐⭐⭐
Speaker	Converts digital audio signals into sound. Quality depends on sound card.	Audio output
Projector	Projects output onto large screen. Types: DLP, LCD Projector, LED Projector. Used in classrooms and conference rooms.	Visual output
Plotter	Specialised large-format output device for engineering/architectural drawings. Draws with pens (continuous lines, not dots). Types: Drum Plotter, Flatbed Plotter.	JKSSB PYQ ⭐
Headphones	Personal audio output — wired or wireless.	Audio

Printers — Impact vs Non-Impact (Most Asked)

Printer Type	Category	Key Facts	Primary Use
Dot Matrix	Impact	Pins strike ink ribbon → dots form characters. Cheapest. Can print on carbon paper (multi-copy). Noisy. Speed: CPS (Characters Per Second).	Bills, multi-copy forms, railway tickets
Daisy Wheel	Impact	Wheel with embossed characters. High quality text. CANNOT print graphics. Slow.	Old typewriter-style quality printing
Line Printer	Impact	Prints one full line at a time. Very fast (LPM — Lines Per Minute). Used in mainframes.	Old mainframe computers
Inkjet	Non-Impact	Sprays tiny ink droplets. Good colour quality. Home use. Speed: PPM. Quality: DPI.	Home photo printing
Laser	Non-Impact	Laser + electrostatic charge + toner powder. Fastest, best quality, most common in offices. Speed: PPM.	Office printing — most common
Thermal	Non-Impact	Uses heat on heat-sensitive paper. No ink required. Used in ATMs, billing counters, POS machines, old fax.	ATM receipts, billing machines
3D Printer	Non-Impact	Creates 3D physical objects layer by layer from digital designs using plastic/resin/metal.	Manufacturing, prototyping

🎯 Printer PYQ Facts — Most Asked:
• Dot Matrix = Impact, cheapest, can do carbon copies, speed = CPS
• Daisy Wheel = Impact, high quality text, CANNOT print graphics
• Laser = Fastest, best quality, offices, uses toner
• Thermal = No ink, heat-sensitive paper, ATMs and billing
• Inkjet = Best for colour photos at home
• Speed: Impact printers = CPS or LPM | Laser/Inkjet = PPM (Pages Per Minute)
• Quality = DPI (Dots Per Inch) — higher = better
• Plotter = draws with pens, used for engineering drawings

6. Secondary Storage Devices

Secondary storage is non-volatile — data is retained permanently even without power. It stores the OS, programs, files and all permanent data.

Storage Device	Key Facts	Primary Use
HDD (Hard Disk Drive)	Magnetic platters + read/write heads. Has moving parts. Capacity: 500GB–20TB. Speed: ~100–200 MB/s. Cheaper per GB than SSD.	Standard storage in desktops/laptops
SSD (Solid State Drive)	Flash memory — no moving parts. Much faster than HDD. More durable. More expensive per GB. Speed: 500MB/s–7GB/s.	Modern laptops, fast desktops
NVMe SSD	Fastest SSD — uses PCIe interface (not SATA). Speed: 3500–7000 MB/s. M.2 form factor.	High-end gaming PCs
USB Flash Drive (Pen Drive)	Portable flash storage. Plug and play. 4GB–1TB.	Data transfer
Memory Card	Portable flash — SD, microSD. Used in cameras, phones.	Cameras, smartphones
CD (Compact Disc)	Optical disc. Capacity: 650–700 MB. Uses laser. Types: CD-ROM (read only), CD-R (write once), CD-RW (rewritable).	Audio, old software
DVD (Digital Versatile Disc)	Optical disc. 4.7GB (single layer), 8.5GB (dual layer). DVD-ROM, DVD-R, DVD-RW.	Movies, backup
Blu-ray Disc	High-definition optical disc. 25GB (single), 50GB (dual layer). Blue-violet laser.	HD/4K movies
Magnetic Tape	Sequential access — very slow but cheapest for bulk archival. 100GB–12TB+ capacity.	Enterprise backup, archival
Cloud Storage	Data on remote servers accessed via internet. Scalable, accessible from anywhere.	Google Drive, OneDrive, iCloud

Storage Units — Data Measurement

Unit	Value
1 Bit	0 or 1 — smallest data unit
1 Nibble	4 bits
1 Byte	8 bits — stores one character
1 Kilobyte (KB)	1024 Bytes
1 Megabyte (MB)	1024 KB
1 Gigabyte (GB)	1024 MB
1 Terabyte (TB)	1024 GB
1 Petabyte (PB)	1024 TB
1 Exabyte (EB)	1024 PB
1 Zettabyte (ZB)	1024 EB

🎯 Storage PYQ Facts:
• HDD = has moving parts (platters + heads) | SSD = no moving parts
• 1 KB = 1024 Bytes — NOT 1000
• CD = 700 MB | DVD = 4.7 GB | Blu-ray = 25 GB
• CD-ROM = read only | CD-R = write once | CD-RW = rewritable
• Magnetic Tape = sequential access, cheapest for archival
• NVMe = fastest SSD (PCIe interface)

7. Motherboard — The Main Circuit Board

The motherboard (also called mainboard or system board) is the primary printed circuit board (PCB) in a computer. All other components connect to it — CPU, RAM, storage, graphics card, ports. It is the communication backbone of the entire computer.

Motherboard Component	Function
CPU Socket	The slot where the processor (CPU) chip is installed. Socket type must match CPU brand/model.
RAM Slots (DIMM)	Slots for installing RAM sticks. Modern motherboards have 2–4 DIMM slots.
PCIe Slots (PCI Express)	High-speed expansion slots for graphics cards (GPU), additional storage, Wi-Fi cards, sound cards.
SATA Connectors	Connects HDD and SATA SSD storage devices to the motherboard.
M.2 Slot	High-speed slot for NVMe SSDs — much faster than SATA.
BIOS/UEFI Chip	ROM chip storing the firmware that runs at startup. BIOS (old) or UEFI (modern replacement).
CMOS Battery	Small coin battery (CR2032) that maintains BIOS settings and system clock when computer is off.
Chipset	Controls communication flow between CPU, RAM, and peripheral devices. North Bridge (fast) + South Bridge (slow) or modern single chipset.
Power Connector (ATX 24-pin)	24-pin connector where the Power Supply Unit (PSU) provides power to motherboard.
USB Headers	Internal connectors for front panel USB ports on the computer case.
Front Panel Connectors	Power button, reset button, HDD activity LED, power LED — connect to PC case buttons.
Audio Connectors	Connects to front panel audio jack on case (headphone + microphone).
CMOS Battery	Small 3V coin battery — maintains date/time and BIOS settings when power is disconnected.

🎯 Motherboard PYQ Facts:
• Motherboard = main circuit board — everything connects here
• BIOS stored in ROM chip on motherboard
• CMOS battery = keeps time and BIOS settings when powered off
• PCIe slot = for graphics card (GPU)
• SATA = connects HDD/SSD | M.2 = connects NVMe SSD
• DIMM slots = for RAM sticks
• Form factors: ATX (standard), Micro-ATX (smaller), Mini-ITX (smallest)

8. Number Systems — Binary, Octal, Decimal & Hexadecimal

Computers process all data in binary (Base-2) — only 0s and 1s. Humans use decimal (Base-10). Other number systems — Octal (Base-8) and Hexadecimal (Base-16) — are used as shorthand for binary in computing.

Number System	Base	Digits Used	Use in Computing	Digits
Decimal	10	0–9	Standard human number system. Used in everyday life.	0,1,2,3,4,5,6,7,8,9
Binary	2	0–1	Computer's native language. All digital data is stored as binary (0 = off/low voltage, 1 = on/high voltage).	0,1
Octal	8	0–7	Shorthand for binary — 3 binary digits = 1 octal digit. Used in Unix file permissions.	0,1,2,3,4,5,6,7
Hexadecimal	16	0–9 + A–F	Shorthand for binary — 4 binary digits = 1 hex digit. Used in memory addresses, HTML colours, debugging.	0–9, A(10), B(11), C(12), D(13), E(14), F(15)

Conversion Quick Reference

Decimal	Binary	Octal	Hexadecimal
0	0000	0	0
1	0001	1	1
2	0010	2	2
3	0011	3	3
4	0100	4	4
5	0101	5	5
6	0110	6	6
7	0111	7	7
8	1000	10	8
9	1001	11	9
10	1010	12	A
11	1011	13	B
12	1100	14	C
13	1101	15	D
14	1110	16	E
15	1111	17	F

Conversion Methods — Exam Shortcuts

Decimal → Binary

Divide by 2 repeatedly. Write remainders bottom-up.
Example: 13 ÷ 2 = 6 r1 → 6 ÷ 2 = 3 r0 → 3 ÷ 2 = 1 r1 → 1 ÷ 2 = 0 r1
13 in Binary = 1101

Binary → Decimal

Multiply each digit by its positional value (powers of 2), right to left: 1,2,4,8,16,32...
Example: 1101 = 1×8 + 1×4 + 0×2 + 1×1 = 8+4+0+1 = 13

Binary → Hex

Group binary digits into sets of 4 from right. Convert each group to hex.
Example: 11011010 → 1101 1010 → D A → DA (hex)

Binary → Octal

Group binary digits into sets of 3 from right. Convert each group to octal.
Example: 110101 → 110 101 → 6 5 → 65 (octal)

🎯 Number System PYQ Facts:
• Computer uses Binary (Base-2) — only 0 and 1
• Hexadecimal uses digits 0–9 and A–F (A=10, B=11, C=12, D=13, E=14, F=15)
• 1 byte = 8 bits — can store values 0–255 in binary
• HTML colour codes are in hexadecimal — e.g., #FF0000 = Red
• Memory addresses shown in hex — e.g., 0x1A2B
• BCD = Binary Coded Decimal — each decimal digit encoded in 4 bits

9. Bus System — Data Highways of the Computer

A bus is a set of electrical wires/pathways that transfer data between computer components — CPU, RAM, storage devices and I/O devices. It is the communication highway of the computer.

Bus Type	Function & Key Facts	Direction
Data Bus	Carries actual data being transferred between components. Bidirectional — data flows in both directions. Width determines how much data can move at once (8-bit, 16-bit, 32-bit, 64-bit).	CPU ↔ RAM, CPU ↔ I/O
Address Bus	Carries memory addresses — tells the system WHERE data is stored in memory. Unidirectional — only CPU sends addresses. Width determines maximum addressable RAM (32-bit = 4GB max RAM).	CPU → RAM (one direction)
Control Bus	Carries control signals — read/write commands, interrupt signals, clock signals. Coordinates all operations.	CPU → all components

Bus Type	Description	Used For
Internal Bus (Local Bus)	Connects CPU to RAM and cache directly. Very high speed. Also called front-side bus or system bus.	Within motherboard
External Bus (Expansion Bus)	Connects CPU to external/peripheral devices. Examples: USB bus, PCIe, SATA, PCI.	CPU to peripherals
USB (Universal Serial Bus)	Most common external bus. Hot-pluggable. USB 2.0 (480 Mbps), USB 3.0 (5 Gbps — blue), USB 3.1 (10 Gbps), USB-C (reversible).	Keyboard, Mouse, Flash drives
PCI / PCIe	Peripheral Component Interconnect / Express. High-speed internal expansion bus for graphics cards, NVMe SSDs, network cards.	GPU, NVMe SSD, Network cards
SATA	Serial ATA — connects HDD and SATA SSD to motherboard. Max speed: 600 MB/s.	HDD, SSD
IDE / PATA	Older parallel interface for storage devices — now obsolete. Replaced by SATA.	Old HDDs (obsolete)
ISA / PCI	Older expansion bus standards — replaced by PCIe.	Legacy systems (obsolete)

🎯 Bus System PYQ Facts:
• Data Bus = carries data (bidirectional)
• Address Bus = carries memory address (unidirectional — CPU only sends)
• Control Bus = carries control signals
• USB 3.0 = Blue coloured port
• Wider data bus = more data per transfer = faster
• Wider address bus = more RAM can be addressed (32-bit = max 4 GB RAM)

10. All JKSSB PYQs — Components of a Computer

Actual questions from JKSSB examinations across all posts — Junior Assistant, FAA, Wildlife Guard/Inspector, Panchayat Secretary, Accounts Assistant, Police SI, Graduate Level.

Q1. JKSSB Junior Assistant PYQ

The CPU stands for:

A) Central Program Unit

B) Computer Processing Unit

C) Central Processing Unit ✅

D) Control Program Unit

Answer: C — CPU = Central Processing Unit — the primary component that executes all instructions. It is called the 'brain of the computer.' It consists of the ALU, Control Unit, and Registers.

Q2. JKSSB Graduate Level PYQ

Which of the following is NOT a component of the CPU?

A) ALU (Arithmetic Logic Unit)

B) Control Unit

C) Registers

D) Hard Disk Drive ✅

Answer: D — Hard Disk Drive (HDD) is a secondary storage device — it is NOT part of the CPU. The CPU consists of three internal components: ALU, Control Unit, and Registers.

Q3. JKSSB FAA PYQ

The ALU (Arithmetic Logic Unit) performs:

A) Only arithmetic operations

B) Only logical operations

C) Both arithmetic and logical operations ✅

D) Memory management

Answer: C — ALU performs BOTH arithmetic operations (addition, subtraction, multiplication, division) AND logical operations (AND, OR, NOT, comparisons). It is the actual computational engine of the CPU.

Q4. JKSSB Accounts Assistant PYQ

The Control Unit of the CPU:

A) Performs all arithmetic calculations

B) Stores data permanently

C) Controls and coordinates the operations of all computer components without doing calculations ✅

D) Manages internet connections

Answer: C — The Control Unit (CU) is the traffic controller of the CPU. It fetches instructions from memory, decodes them, and directs all other components. It does NOT perform calculations — that is the ALU's job.

Q5. JKSSB Graduate Level PYQ

Which memory type is the FASTEST in a computer system?

A) RAM

B) Hard Disk

C) CPU Registers ✅

D) ROM

Answer: C — CPU Registers are the fastest memory — they are located inside the CPU chip itself and hold data currently being processed. Speed hierarchy: Registers > Cache > RAM > SSD > HDD.

Q6. JKSSB Junior Assistant PYQ

RAM is described as 'volatile' because:

A) It can catch fire if overheated

B) Data stored in it is lost when the computer is turned off ✅

C) It stores data permanently

D) It is faster than ROM

Answer: B — RAM is volatile — meaning all data stored in it is lost when power is removed (computer turned off). This is why we save work to the hard disk before shutting down. ROM is non-volatile.

Q7. JKSSB Accounts Assistant PYQ

EPROM can be erased using:

A) Electric current

B) Ultraviolet (UV) light ✅

C) Magnetic fields

D) High temperature

Answer: B — EPROM (Erasable Programmable ROM) is erased using ultraviolet (UV) light. EEPROM (Electrically Erasable PROM) is erased using electric current and is the basis of modern Flash memory (USB drives, SSDs).

Q8. JKSSB FAA PYQ

OMR technology is specifically used to:

A) Read text from printed documents

B) Read magnetic ink characters on cheques

C) Detect marks made by pen or pencil in predefined positions — used for MCQ answer sheets ✅

D) Scan barcodes on products

Answer: C — OMR = Optical Mark Recognition. It detects marks (filled circles/bubbles) made by pen or pencil in predefined positions. Used primarily for checking MCQ answer sheets. It CANNOT read handwriting or actual text.

Q9. JKSSB Graduate Level PYQ

MICR is used in which sector?

A) Education — for checking exam papers

B) Banking — for reading cheque details ✅

C) Retail — for scanning product barcodes

D) Healthcare — for patient records

Answer: B — MICR (Magnetic Ink Character Recognition) reads characters printed with magnetic ink. It is used exclusively in banking — to read account numbers, cheque numbers and bank codes printed at the bottom of bank cheques.

Q10. JKSSB Wildlife Inspector 2026 PYQ

Which printer type CANNOT print graphics?

A) Dot Matrix Printer

B) Laser Printer

C) Daisy Wheel Printer ✅

D) Inkjet Printer

Answer: C — Daisy Wheel Printer has pre-formed characters embossed on petals of a wheel — it can only print those specific characters. It CANNOT print graphics because it has no mechanism to form arbitrary shapes.

Q11. JKSSB Panchayat Secretary PYQ

Thermal printers are commonly used in:

A) Large printing press for newspapers

B) ATM machines and POS billing counters ✅

C) Architectural drawing plotters

D) Photo development labs

Answer: B — Thermal printers use heat on heat-sensitive paper — they require NO INK or toner. This makes them ideal for ATM receipt machines and Point of Sale (POS) billing counters where continuous, fast, low-maintenance printing is needed.

Q12. JKSSB Graduate Level PYQ

A Plotter is an output device used for:

A) Printing high-speed text documents

B) Printing large-format engineering drawings and blueprints ✅

C) Scanning physical documents

D) Playing audio output

Answer: B — A Plotter is a specialised output device for large-format vector graphics — architectural drawings, engineering blueprints, maps and CAD designs. Unlike printers that form images from dots, plotters draw continuous lines using pens.

Q13. JKSSB Junior Assistant PYQ

What is the decimal equivalent of the binary number 1010?

A) 8

B) 10 ✅

C) 12

D) 14

Answer: B — Binary 1010 = 1×8 + 0×4 + 1×2 + 0×1 = 8+0+2+0 = 10 in decimal. Remember: binary positional values from right to left are 1, 2, 4, 8, 16, 32...

Q14. JKSSB Graduate Level PYQ

Which of the following correctly represents the number 15 in hexadecimal?

A) E

B) F ✅

C) G

D) 10

Answer: B — In hexadecimal, digits go 0–9 then A(10), B(11), C(12), D(13), E(14), F(15). So 15 in decimal = F in hexadecimal.

Q15. JKSSB FAA PYQ

USB 3.0 ports are identified by their:

A) Red colour

B) Yellow colour

C) Blue colour ✅

D) Green colour

Answer: C — USB 3.0 ports are coloured BLUE to distinguish them from USB 2.0 ports (which are black or white). USB 3.0 transfers data at up to 5 Gbps (compared to USB 2.0's 480 Mbps).

Q16. JKSSB Junior Assistant PYQ

SSD is faster than HDD because:

A) SSD uses larger platters

B) SSD has more moving parts

C) SSD has no moving parts — it uses flash memory chips ✅

D) SSD is connected via USB

Answer: C — SSD (Solid State Drive) uses flash memory chips with NO moving mechanical parts. HDD uses spinning magnetic platters with mechanical read/write heads. Absence of moving parts makes SSD significantly faster, lighter and more durable.

Q17. JKSSB Graduate Level PYQ

The motherboard is also called the:

A) Central Processing Board

B) Main Circuit Board / Mainboard / System Board ✅

C) Graphics Processing Board

D) Network Interface Board

Answer: B — The motherboard is also called the mainboard or system board. It is the primary printed circuit board (PCB) to which all other components — CPU, RAM, storage, GPU — connect.

Q18. JKSSB FAA PYQ

1 Kilobyte is equal to:

A) 1000 Bytes

B) 1024 Bytes ✅

C) 512 Bytes

D) 2000 Bytes

Answer: B — 1 KB = 1024 Bytes (2^10). This is because computers use binary (base-2) counting, not decimal. Similarly: 1 MB = 1024 KB, 1 GB = 1024 MB.

Q19. JKSSB Panchayat Secretary PYQ

The binary number system uses:

A) Digits 0–7

B) Digits 0–9

C) Only digits 0 and 1 ✅

D) Digits 0–9 and A–F

Answer: C — Binary (Base-2) uses only TWO digits — 0 and 1. All computer data is stored and processed in binary form. 0 = off/low voltage, 1 = on/high voltage.

Q20. JKSSB Graduate Level PYQ

What does the Data Bus in a computer do?

A) Carries memory address locations only

B) Carries control signals for read/write operations

C) Carries actual data being transferred between components ✅

D) Provides power to all components

Answer: C — The Data Bus carries the actual data being transferred between the CPU, RAM, and other components. It is bidirectional. The Address Bus carries memory addresses (unidirectional). The Control Bus carries control signals.

Q21. JKSSB Wildlife Inspector 2026 PYQ

A Touch Screen is classified as:

A) An input device only

B) An output device only

C) Both input and output device ✅

D) A storage device

Answer: C — A Touch Screen is BOTH an input device (it accepts touch input from fingers or stylus) AND an output device (it displays visual output like a monitor). It is therefore an Input-Output (I/O) device.

Q22. JKSSB Graduate Level PYQ

Virtual memory in Windows is stored as:

A) BIOS.sys

B) bootmgr.exe

C) pagefile.sys ✅

D) RAM.cache

Answer: C — Virtual memory in Windows is stored in a file called pagefile.sys on the hard disk (usually C:\pagefile.sys). Linux uses a swap partition or swap file. Virtual memory uses HDD space as an extension of RAM.

Q23. JKSSB Accounts Assistant PYQ

Which of the following is the correct full form of SRAM?

A) Serial Random Access Memory

B) Static Random Access Memory ✅

C) Stored Random Access Memory

D) Synchronous RAM

Answer: B — SRAM = Static Random Access Memory. It does not need to be periodically refreshed (unlike DRAM). It is faster and more expensive than DRAM. Used for CPU Cache memory (L1/L2/L3).

Q24. JKSSB Junior Assistant PYQ

The Joystick is primarily used as a:

A) Output device

B) Input device ✅

C) Storage device

D) Processing device

Answer: B — A Joystick is an input device — it sends directional control input (up, down, left, right) to the computer. Primarily used in gaming, flight simulators and industrial control systems.

Q25. JKSSB Graduate Level PYQ

CRT monitor technology uses:

A) Liquid crystals and a backlight

B) Self-illuminating organic diodes

C) An electron gun firing electrons at a phosphor-coated screen ✅

D) LED matrix panels

Answer: C — CRT (Cathode Ray Tube) monitors use an electron gun that fires a beam of electrons at a phosphor-coated screen — the phosphors glow to form the image. CRTs are large, heavy and power-hungry. Now replaced by LCD/LED monitors.

11. New Statement-Based Pattern MCQs

JKSSB 2026 new pattern — evaluate multiple statements simultaneously.

Q1. JKSSB New Pattern STATEMENT BASED

Which of the following statements about the CPU are CORRECT?

I. The ALU performs both arithmetic and logical operations

II. The Control Unit performs all calculations in the CPU

III. Registers are the fastest memory in a computer system

IV. CPU speed is measured in GHz (Gigahertz)

A) I, III and IV only ✅

B) All of the above

C) I and II only

D) II, III and IV only

Answer: A — Statements I, III, IV are correct. Statement II is WRONG — the Control Unit does NOT perform calculations; it controls and coordinates. The ALU does the actual computing.

Q2. JKSSB New Pattern STATEMENT BASED

Identify the INCORRECT statements about RAM and ROM:

I. RAM is volatile — data is lost when power is switched off

II. ROM stores the BIOS firmware and is non-volatile

III. SRAM is used for main system RAM because it is cheaper than DRAM

IV. EPROM is erased using ultraviolet (UV) light

A) III only ✅

B) I and II only

C) II and IV only

D) All are incorrect

Answer: A — Statement III is WRONG — SRAM is used for CACHE (not main system RAM) because it is FASTER but MORE EXPENSIVE than DRAM. Main system RAM uses DRAM (cheaper, denser). Statements I, II, IV are correct.

Q3. JKSSB New Pattern STATEMENT BASED

Which statements about printers are CORRECT?

I. Dot Matrix is an impact printer that can print on carbon/multi-copy paper

II. Daisy Wheel printers can print both text and graphics

III. Thermal printers do not require ink — they use heat-sensitive paper

IV. Laser printers are the fastest and produce the best quality output

A) I, III and IV only ✅

B) All of the above

C) I and II only

D) II and IV only

Answer: A — Statements I, III, IV are correct. Statement II is WRONG — Daisy Wheel printers CANNOT print graphics because they only have pre-formed characters on the wheel. This is one of the most commonly tested facts about printers.

Q4. JKSSB New Pattern STATEMENT BASED

Consider the following about number systems:

I. Computers use binary (base-2) — only digits 0 and 1

II. Hexadecimal uses base-16 — digits 0–9 and A–F where F represents 15

III. Binary number 1010 equals 10 in decimal

IV. Octal number system uses digits 0–9

A) I, II and III only ✅

B) All of the above

C) I and III only

D) II, III and IV only

Answer: A — Statements I, II, III are correct. Statement IV is WRONG — Octal uses digits 0–7 (eight digits, 0 through 7), NOT 0–9. Decimal uses 0–9. Octal = Base-8.

Q5. JKSSB New Pattern STATEMENT BASED

Which of the following statements about storage devices are CORRECT?

I. SSD has no moving parts and is faster than HDD

II. 1 Kilobyte equals 1024 Bytes

III. HDD uses flash memory for storing data

IV. CD-ROM is a read-only optical disc with 700MB capacity

A) I, II and IV only ✅

B) All of the above

C) I and III only

D) II and IV only

Answer: A — Statements I, II, IV are correct. Statement III is WRONG — HDD uses MAGNETIC platters (spinning disks with read/write heads), NOT flash memory. SSDs use flash memory. This is one of the most common errors made by students.

Q6. JKSSB New Pattern STATEMENT BASED

Select the CORRECT statements about input devices:

I. OMR can read both marks AND handwritten text

II. MICR is used in banking to read cheque details printed in magnetic ink

III. A Touch Screen is both an input and output device

IV. The mouse was invented by Douglas Engelbart

A) II, III and IV only ✅

B) All of the above

C) I and II only

D) I, III and IV only

Answer: A — Statements II, III, IV are correct. Statement I is WRONG — OMR can ONLY read marks (filled bubbles/circles) in predefined positions. It CANNOT read handwriting or actual text. OCR is the technology that reads text.

⚡ Quick Revision — Most Exam-Tested Facts

CPU

• CPU = ALU + CU + Registers
• ALU = arithmetic + logical
• CU = controls (no calculation)
• Registers = fastest memory
• Speed = GHz | Perf = MIPS
• Intel & AMD = main makers

Memory

• RAM = volatile (loses on power off)
• ROM = non-volatile (permanent)
• SRAM = Cache | DRAM = main RAM
• EPROM erased by UV light
• EEPROM erased by electricity
• 1 KB = 1024 Bytes

Input/Output

• OMR = marks only (no handwriting)
• OCR = reads text
• MICR = banking/cheques
• Touch Screen = Input + Output
• Daisy Wheel = NO graphics
• Thermal = no ink (ATMs)
• Plotter = engineering drawings

Number Systems

• Binary = Base-2 (0,1)
• Octal = Base-8 (0–7)
• Decimal = Base-10 (0–9)
• Hex = Base-16 (0–9, A–F)
• F in Hex = 15 in Decimal
• 1010 binary = 10 decimal
• SSD = no moving parts, faster

Tags

#JKSSB#ComponentsOfComputer#CPU#ALU#ControlUnit#RAM#ROM#InputDevices#OutputDevices#Storage#Motherboard#NumberSystems#BinarySystem#HDD#SSD#OMR#OCR#MICR#Printers#ComputerNotes#JKPSC#FAA2026#JuniorAssistant#PoliceExam#JKEdusphere