🖨️ Computer Hardware & Output Devices

Input Devices — Quick Reference

An input device sends data and instructions INTO the computer for processing.

Device	Type	How It Works
Keyboard	Manual	Keys pressed to enter characters
Mouse	Pointing	Click, drag, scroll to interact with GUI
Scanner	Optical	Converts physical documents to digital images
Microphone	Audio	Converts sound waves to digital audio
Webcam	Video	Captures video input for calls/recording
Touchscreen	Direct	Touch-based input (phones, ATMs, kiosks)
Barcode Reader	Optical	Reads printed barcodes (shops, warehouses)
OMR	Optical	Optical Mark Recognition — reads pencil marks (exam sheets)
OCR	Optical	Optical Character Recognition — reads printed/handwritten text
MICR	Magnetic	Magnetic Ink Character Recognition — reads cheque numbers
Light Pen	Pointing	Pen-shaped device to select on screen (old CRT monitors)
Joystick	Pointing	Gaming/control device with stick movement
Trackball	Pointing	Stationary ball rotated by fingers (like inverted mouse)

Keep the usage difference clear: OMR is used for marked answer sheets, OCR turns printed text into editable digital text, and MICR is used in cheque processing.

The most common keyboard layout in personal computers is QWERTY, named after the first six letters of the top alphabet row. Examiners sometimes ask this as a direct one-line fact.

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CPU — Central Processing Unit

The CPU is the "brain" of the computer. It performs all processing — calculations, comparisons, and decision-making.

CPU Components

Component	Full Form	Function
ALU	Arithmetic Logic Unit	Performs arithmetic (+, -, x, /) and logical (AND, OR, NOT) operations
CU	Control Unit	Directs and coordinates all CPU operations; fetches and decodes instructions
Registers	—	Ultra-fast temporary storage inside CPU

Important CPU Registers

Register	Full Form	Purpose
MAR	Memory Address Register	Holds address of memory location to be accessed
MDR	Memory Data Register	Holds data being read from or written to memory
PC	Program Counter	Holds address of the next instruction to execute
IR	Instruction Register	Holds the current instruction being executed
Accumulator	—	Stores intermediate results of ALU operations

A simple way to remember the CPU parts is this: ALU handles calculations and logic, the Control Unit directs the work, and registers hold the fastest temporary data.

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Motherboard Components

The motherboard is the main circuit board that connects all computer components together.

Component	Purpose
Chipset	Controls data flow between CPU, RAM, and peripherals
RAM Slots	Where RAM modules are inserted
PCI Slot	Peripheral Component Interconnect — for expansion cards
PCIe Slot	PCI Express — faster, modern version (for GPU, SSD)
CMOS Battery	Keeps BIOS settings and clock running when PC is off
BIOS/UEFI	Basic Input Output System — firmware that boots the computer

Ports on a Computer

Port	Full Form	Purpose
USB	Universal Serial Bus	Connect peripherals (pen drive, mouse, printer)
HDMI	High-Definition Multimedia Interface	Video + audio to monitor/TV
VGA	Video Graphics Array	Older video output (analog)
Ethernet (RJ-45)	—	Wired internet/LAN connection
Audio Jack (3.5mm)	—	Headphones, microphone, speakers
PS/2	—	Old keyboard/mouse port (green = mouse, purple = keyboard)

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Output Devices

An output device displays or produces the processed results from the computer.

A soft copy is output seen in digital form on a screen, such as text on a monitor or a PDF viewed on a phone. A hard copy is the physical printed version of that output on paper.

Monitor Types

Type	Full Form	Technology	Key Feature
CRT	Cathode Ray Tube	Electron beam on phosphor screen	Bulky, old, cheap
LCD	Liquid Crystal Display	Liquid crystals with backlight	Thin, low power
LED	Light Emitting Diode	LCD with LED backlight	Brighter, energy efficient
OLED	Organic LED	Each pixel emits own light	Best contrast, thinnest

Monitor Specifications:

Term	Meaning
Resolution	Number of pixels (e.g., 1920x1080 = Full HD)
Refresh Rate	How many times screen updates per second (60Hz, 144Hz)
Pixel	Smallest unit of display — a single dot of color
Aspect Ratio	Width:Height ratio (16:9 widescreen, 4:3 old monitors)

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Printers

Printers produce hard copy (physical paper output) of digital documents.

Impact vs Non-Impact Printers

Feature	Impact Printers	Non-Impact Printers
Mechanism	Physical contact — strikes ribbon against paper	No physical contact — uses laser/ink/heat
Noise	Very noisy	Quiet
Speed	Slow	Fast
Quality	Lower	Higher
Carbon copies	Can make carbon copies	Cannot make carbon copies
Cost per page	Low	Varies
Examples	Dot-matrix, Daisy wheel, Line printer	Laser, Inkjet, Thermal

Impact Printers

Dot-Matrix Printer

• Uses a print head with pins (9 or 24 pins) that strike an ink ribbon against paper
• Creates characters as a pattern of dots
• Can print on multi-part/carbon copy forms (used in billing, railways)
• Noisy but cheap to operate

Daisy Wheel Printer

• Uses a wheel with character petals (like a daisy flower)
• Produces letter-quality print (typewriter quality)
• Cannot print graphics — only pre-formed characters
• Very slow, now obsolete

Line Printer

• Prints an entire line at once — very fast
• Used in mainframe environments for bulk printing
• Types: drum printer, chain printer, band printer

Non-Impact Printers

Laser Printer

• Uses a laser beam to create image on a photosensitive drum
• Toner (dry powder) is fused onto paper using heat
• Fastest and highest quality for text documents
• Invented at Xerox PARC
• Cost: High initial cost, low per-page cost

Inkjet Printer

• Sprays tiny droplets of liquid ink through nozzles onto paper
• Excellent for color printing and photos
• Cost: Low initial cost, high ink cartridge cost
• Slower than laser for large volumes

Thermal Printer

• Uses heat on special thermal paper
• Common in: ATM receipts, POS billing, labels
• No ink or toner needed — paper itself changes color with heat
• Print fades over time

Printer Comparison Table

Feature	Dot-Matrix	Laser	Inkjet	Thermal
Technology	Pins + ribbon	Laser + toner	Liquid ink + nozzles	Heat on thermal paper
Speed	Slow	Fastest	Moderate	Fast (for receipts)
Quality	Low	Highest	High (photos)	Moderate
Color	Limited	Yes (expensive)	Best for color	No
Noise	Very noisy	Quiet	Quiet	Quiet
Carbon Copy	Yes	No	No	No
Use Case	Billing, railways	Office documents	Photos, home use	Receipts, labels

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PostScript and PCL

Technology	Developer	Description
PostScript	Adobe	Page Description Language — tells printer exactly how to render text, graphics, and images. Device-independent
PCL	HP (Hewlett-Packard)	Printer Command Language — simpler, faster, device-dependent. Most common for office printing

PostScript vs PCL:

• PostScript: better for complex graphics, publishing, and design work
• PCL: faster for standard text documents and office use

Printer Specifications

Term	Full Form	Meaning
DPI	Dots Per Inch	Print quality/resolution — higher = sharper
PPM	Pages Per Minute	Print speed

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Plotter

A plotter is a specialized output device for printing large-format technical drawings, blueprints, maps, and banners.

Type	How It Works
Pen Plotter	Uses pens to draw lines on paper — precise line drawings
Electrostatic Plotter	Uses electrical charge to create image — faster
Inkjet Plotter	Large-format inkjet — for posters, banners

Plotter vs Printer:

• Plotter = large format, vector graphics, continuous lines (engineering drawings)
• Printer = standard size (A4/A3), raster graphics, text documents

Other Output Devices

Device	Function
Speaker	Produces audio output (music, alerts, voice)
Projector	Displays enlarged image on screen/wall (presentations)
Headphones	Personal audio output
3D Printer	Builds three-dimensional objects layer by layer from a digital model (additive manufacturing)

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Input Device Details

OMR (Optical Mark Recognition)

OMR reads pencil marks on pre-printed forms. It detects the presence or absence of a mark in predefined positions. Used extensively in competitive exam answer sheets, surveys, and election ballots.

OCR (Optical Character Recognition)

OCR converts printed or handwritten text into machine-readable digital text. Used in digitising books, reading number plates, and scanning documents.

MICR (Magnetic Ink Character Recognition)

MICR reads characters printed with special magnetic ink. Used primarily in bank cheque processing to read cheque numbers, bank codes, and account numbers.

Barcode Reader vs QR Code Reader

Feature	Barcode Reader	QR Code Reader
Data Format	1D — horizontal lines of varying width	2D — square matrix of black/white modules
Data Capacity	Up to ~100 characters	Up to ~4,000+ characters
Stores	Only numbers/text	Text, URLs, images, contact info
Used In	Retail products, inventory	UPI payments, tickets, websites
Reader	Laser/CCD scanner	Camera-based (smartphone)

Touch Screen Types

Type	Resistive	Capacitive
How it Works	Two flexible layers pressed together by touch	Senses electrical charge from human finger
Accuracy	Lower	Higher
Multi-touch	No	Yes
Stylus/Gloves	Works with any object	Only bare finger or special stylus
Used In	ATMs, older devices, industrial	Smartphones, tablets, modern touchscreens

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SMPS — Power Supply Unit

SMPS (Switch Mode Power Supply) converts AC (Alternating Current) from the wall socket into DC (Direct Current) required by computer components. It provides different voltages:

Voltage	Components Powered
+3.3V	RAM, chipset, some CPU circuits
+5V	USB ports, SSD, logic circuits
+12V	CPU, GPU, cooling fans, hard drives

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USB Types — Speed Comparison

USB Version	Year	Maximum Speed	Connector Type
USB 1.0	1996	1.5 Mbps (Low Speed)	Type-A
USB 1.1	1998	12 Mbps (Full Speed)	Type-A
USB 2.0	2000	480 Mbps (Hi-Speed)	Type-A, Mini, Micro
USB 3.0	2008	5 Gbps (SuperSpeed)	Type-A (blue), Type-B
USB 3.1	2013	10 Gbps	Type-A, Type-C
USB-C	2014+	10–40 Gbps	Reversible Type-C connector

In practical terms, USB 2.0 is much slower than USB 3.0, while USB-C refers to the newer reversible connector shape that can support very high modern transfer speeds.

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Port Types — Complete Reference

Port	Type	Purpose
Serial Port	Data (one bit at a time)	Older modems, mice (DB-9 connector)
Parallel Port	Data (multiple bits at once)	Older printers (DB-25 connector)
PS/2	Input	Old keyboard (purple) and mouse (green)
VGA	Video (analog)	Older monitors — 15-pin connector
DVI (Digital Visual Interface)	Video (digital/analog)	Monitors — better than VGA
HDMI	Video + Audio (digital)	Modern monitors, TVs, projectors
DisplayPort	Video + Audio (digital)	High-end monitors, gaming displays
Ethernet (RJ-45)	Network	Wired LAN/internet connection
Audio Jack (3.5mm)	Audio	Headphones, microphone, speakers

Serial ports send one bit at a time, whereas parallel ports send multiple bits together. Both have largely been replaced in everyday use by USB.

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Printer Resolution and Speed

Term	Full Form	Meaning	Example
DPI	Dots Per Inch	Print quality/resolution — higher DPI = sharper image	300 DPI (basic), 1200 DPI (high quality)
PPM	Pages Per Minute	Print speed — higher PPM = faster printing	Laser: 20-60 PPM; Inkjet: 5-20 PPM

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Summary Points

Concept	Key Details
ALU	Arithmetic + Logic operations in CPU
CU	Controls and coordinates all CPU operations
MAR	Memory Address Register — holds address
MDR	Memory Data Register — holds data
PC	Program Counter — address of next instruction
IR	Instruction Register — current instruction
Accumulator	Stores intermediate ALU results
OMR	Reads pencil marks — exam sheets
OCR	Reads printed/handwritten text — digitising books
MICR	Reads magnetic ink — bank cheques
Barcode	1D lines, ~100 chars, laser/CCD scanner — retail
QR Code	2D matrix, 4000+ chars, camera-based — UPI payments
Resistive Touch	Works with any object, no multi-touch — ATMs, industrial
Capacitive Touch	Bare finger only, multi-touch — smartphones, tablets
CRT	Old bulky monitor — cathode ray tube
LCD/LED/OLED	Modern thin monitors (OLED = best contrast, each pixel emits light)
Dot-Matrix	Impact, 9/24 pins + ribbon, noisy, carbon copies — billing, railways
Laser Printer	Toner + photosensitive drum, fastest, best text quality (Xerox PARC)
Inkjet Printer	Liquid ink + nozzles, best for color/photos
Thermal	Heat on special paper, no ink — ATM receipts, print fades
PostScript	Adobe's page description language — complex graphics
PCL	HP's Printer Command Language — office printing
DPI	Dots Per Inch — print quality (300 basic, 1200 high)
PPM	Pages Per Minute — print speed (Laser 20-60, Inkjet 5-20)
Plotter	Large-format output — engineering drawings, pen/electrostatic/inkjet
3D Printer	Layer-by-layer additive manufacturing from digital model
SMPS	AC→DC conversion — 3.3V (RAM), 5V (USB), 12V (CPU/GPU/fans)
USB 1.0	1996, 1.5 Mbps (Low Speed)
USB 2.0	2000, 480 Mbps (Hi-Speed)
USB 3.0	2008, 5 Gbps (SuperSpeed)
USB-C	2014+, 10-40 Gbps, reversible connector
VGA	Analog video, 15-pin — older monitors
DVI	Digital Visual Interface — better than VGA
HDMI	Digital video + audio — monitors, TVs, projectors
DisplayPort	High-end digital video + audio — gaming displays
RJ-45	Ethernet port — wired LAN/internet
Serial Port	Sends one bit at a time (old modems, DB-9)
Parallel Port	Sends multiple bits at once (old printers, DB-25)