Input and Output Devices

1. Introduction to Input & Output Devices

• Purpose: Input and output devices are used to establish communication between the computer and the human user.
• Workflow:
  1. The user provides data and instructions using input devices.
  2. The computer processes this input data.
  3. The computer provides the final result to the user via output devices.
• Peripheral Devices: All input and output devices connected to the computer machine are collectively known as Peripheral Devices.

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2. Input Devices

• Definition: Devices used by the user to provide data and instructions to the computer are called Input Devices.
• Key Function: Since the computer only understands binary, input devices take data from the user, convert it into Machine Language, and send this converted data to the CPU for processing.

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3. The Keyboard (Primary Input Device)

• Overview: The keyboard is one of the most essential main input devices, resembling a standard typewriter but equipped with many more keys.
• Usage: It is primarily used to feed alphabetical and numerical data/information into the computer.
• Common Layouts: The most commonly used keyboard layouts are QWERTY, DVORAK, and AZERTY.

How the Keyboard Works (Internal Mechanism)

• When a key is pressed, the keyboard establishes communication with the Keyboard Controller and the Keyboard Buffer.
• The keyboard controller takes the code of the pressed key and stores it temporarily in the keyboard buffer.
• The code stored in the buffer is then sent to the CPU.
• After the CPU processes this code, the result is displayed on the output device (e.g., monitor).

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4. Types of Keys on a Keyboard

Keyboards consist of various categories of keys, each serving a distinct purpose:

• 1. Alphanumeric Keys: These include all alphabet letters (A-Z, a-z) and basic numbers (0-9).
• 2. Numeric Keys (Keypad): Located on the far right side of the keyboard. They consist of numbers (0-9) and mathematical operators ($+$, $-$, $*$, $/$) for quick calculations.
• 3. Function Keys: Also known as Programmable Keys.
  • They are used to instruct the computer to perform specific, pre-programmed tasks.
  • They are located at the very top of the keyboard, above the alphanumeric keys, and are labeled from F1 to F12.
• 4. Control Keys (e.g., Ctrl): These keys are used in combination with other keys to perform special shortcut tasks.
  • Example: Pressing Ctrl + S together is used to save a document.

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5. Cursor Control Keys (Navigation)

These keys are used to control the movement of the cursor on the screen.

• Arrow Keys: Four keys marked with arrows pointing in four directions (Left, Right, Up, Down).
  • They are arranged in an inverted 'T' shape between the alphanumeric and numeric keypads.
  • Used to move the cursor step-by-step in any direction.

Advanced Cursor Control Keys (Comparison Table) 

• Home: Moves the cursor immediately to the beginning of the current line or the start of the document
• End: Moves the cursor immediately to the end of the current line.
• Page Up: Shifts the page view up by one full screen; moves the cursor to the previous page.
• Page Down: Shifts the page view down by one full screen; moves the cursor to the next page.
• Enter Key: Considered the main key of the keyboard. It is used to send typed instructions to the computer for execution. Exam Tip: Pressing 'Enter' is also an alternative way to press an "OK" button.
• Shift Key: Many keys have two symbols printed on them (top and bottom); the Shift key is held down to type the upper symbol. It is also known as a Combination Key because it is always used in conjunction with other keys.
• Escape (Esc) Key: Used to immediately stop, cancel, or exit any ongoing task. Shortcut: Pressing Ctrl + Esc together opens the computer's Start Menu.
• Backspace Key: Erases typed data or information, moving from the right side towards the left side.
• Delete Key: Deletes information and characters from the screen and memory. Exam Tip: Pressing Shift + Delete permanently removes a selected file from the computer's memory.
• Caps Lock Key: Used to type the alphabet in capital letters. When enabled (active), letters type in capitals; when disabled, they type in small letters.
• Spacebar Key: Creates space between two words or letters. It is the longest key on the entire keyboard.
• Num Lock Key: Enables or disables the numeric keypad. Numbers can only be typed using the keypad when this key is active.
• Window Key: Directly opens the Start Menu.
• Tab Key: Jumps the cursor forward by five spaces at a time. Shortcut: Pressing Shift + Tab brings the cursor back by five spaces. It is also used to indent paragraphs.

Classification of Special Keys (Quick Revision Table)

Key Category	Examples from Keyboard	Reason for Name / Main Function
Toggle Keys	Caps Lock, Num Lock	They toggle (switch) between two states (On/Off) every time they are pressed.
Combination Keys	Shift	They are used together with other keys to perform specific actions.
Largest Key	Spacebar	The longest physical key on the board, used for spacing.

Important Fact: A standard QWERTY keyboard generally consists of 104 keys.

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2. Pointing Devices

• Definition: Pointing devices are hardware tools used to move the cursor or pointer from one place to another on the monitor's screen.
• Common Examples: Mouse, Trackball, Joystick, Light Pen, and Touch Screen.

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3. The Mouse

• Overview: The mouse is the most common pointing device. It controls the cursor (the blinking line indicating your text position) or the pointer on the screen. It is also used to give instructions to the computer via graphics.
• Invention Fact: Invented by Douglas C. Engelbart in 1963 at the Stanford Research Center.
• Physical Structure: A standard mouse usually has two or three buttons:
  1. Left Button
  2. Right Button
  3. Scroll Wheel: Located between the left and right buttons, used to move/scroll page contents up or down.

Types of Mouse

There are three main types of mice commonly used:

1. Wireless Mouse
2. Mechanical Mouse
3. Optical Mouse

Primary Mouse Functions (Actions)

• Click (or Left Click): Used to select an object or item on the screen.
• Double Click: Used to open a selected document, file, or program
• Right-Click: Displays a list of commands or a menu on the screen. It is primarily used to access the properties or settings of a selected object.
• Drag and Drop: Used to move an object, file, or icon from one location to another on the screen.

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2. Trackball

• Definition: A pointing device that functions very similarly to a mouse.
• Design: Instead of moving the whole device, it has a ball located on its upper surface. The user rolls this ball to control the movement of the cursor on the screen.
• Major Applications:
  • CAD Workstations: Computer-Aided Design.
  • CAM Workstations: Computer-Aided Manufacturing.
  • Computerised Control Rooms: Air-traffic control rooms and radar controls.
  • Naval Use: Sonar systems on ships.

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3. Joystick

• Definition: A pointing device equipped with a handle that can move in all directions to control cursor movement.
• Major Applications: Highly popular in flight simulators, computer gaming, and CAD/CAM systems.

Comparison Table: Mouse vs. Joystick

Feature	Mouse	Joystick
Cursor Control	Cursor movement directly depends on the physical movement of the mouse itself.	The pointer continuously moves in the direction the handle is pointed and is controlled by the handle.
Primary Use	General computing, selecting, and opening files.	Gaming, flight simulators, and specialized CAD/CAM controls.

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4. Light Pen

• Definition: A handheld, electro-optical pointing device.
• Design: It contains a small tube with a built-in Photocell.
• How it Works: When the pen is brought close to the screen, it senses the light and generates an electrical pulse to identify specific locations on the screen. Note: It provides no information if placed on a blank/empty screen area.
• Primary Uses:
  • Creating drawings and graphics.
  • Selecting menu options.
  • Commonly used with PDAs (Personal Digital Assistants).

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5. Touch Screen

• Definition: An input device that registers input when a user touches the computer screen directly with their fingers.
• Major Applications:
  • ATMs (Automated Teller Machines).
  • Airline Reservation kiosks.
  • Banks and Supermarkets.
  • Mobile phones and tablets.

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6. Digitizers and Graphic Tablets

• Definition: Special input devices equipped with commands that convert physical drawings, sketches, and photos into digital signals.
• Primary Use: It allows artists and designers to create hand-drawn images and graphic designs directly on a computer.

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7. Bar Code Reader

• Definition: An input device used specifically to read barcodes (also known as the Universal Product Code or UPC) printed on product labels.
• How it Works:
  • It emits a light beam onto the barcode image.
  • A light-sensitive detector inside the reader recognizes the barcode from both sides.
  • It then converts this scanned data into a Numeric Code that the computer can process.
• What is a Barcode?: Barcodes are a series of vertical lines made of dark and light ink that represent information in a machine-readable format.
• Primary Use: Extensively used in supermarkets and retail stores to quickly and easily read product prices during checkout.

 

8. Optical Mark Reader (OMR)

• Definition: An OMR is a type of optical input device used to identify and read marks made on a piece of paper.
• How it Works: It emits a beam of light onto the paper. It reads the specific marks where the light falls and sends this data as input to the computer.
• Primary Application: It is extensively used to check the answer sheets of Objective Type (multiple-choice) examinations.
• Advantage: It can effortlessly evaluate thousands of question answers in a very short amount of time.

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9. Optical Character Recognition (OCR)

• Definition: OCR is an upgraded and advanced version of the OMR.
• Key Feature: Unlike OMR which only reads simple marks, OCR can read printed text as well as clearly handwritten characters.
• How it Works: It uses a light source to recognize the exact shape of the characters, a technology known as Optical Character Recognition.
• Performance Speed: Extremely fast, capable of reading 1500 to 3000 characters per second.
• Major Applications:
  • Reading and digitizing old physical documents.
  • Processing telephone bills, electricity bills, and insurance premiums.

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10. Magnetic Ink Character Reader (MICR)

• Definition: MICR is an input device that examines the shape of information in a matrix format, reads it, and sends the data to the computer.
• Magnetic Ink Concept: The characters read by MICR are printed using a special ink containing Iron Particles. Because these particles can be magnetized, the ink is known as Magnetic Ink.
• Primary Application: Primarily used in the Banking Sector. It is used to identify and process the magnetic encoding numbers printed at the very bottom of bank cheques.

Comparison Table: OMR vs. OCR vs. MICR (Quick Revision)

Feature	OMR (Optical Mark Reader)	OCR (Optical Character Recognition)	MICR (Magnetic Ink Character Reader)
What it Reads	Simple pencil/pen marks.	Printed or cleanly handwritten letters/characters.	Special characters printed with magnetic iron-particle ink.
Primary Use-Case	Grading Objective-type exams.	Reading old documents, utility bills, and insurance premiums.	Processing cheques in Banks.

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11. Smart Card Reader

• Definition: A device used specifically to access the microprocessor embedded within a smart card.
• Material & Usage: Smart cards are generally made of plastic and are heavily used by large companies and organizations for high-level security purposes.

Types of Smart Cards

Card Type	Key Components & Functionality
1. Memory Card	Contains non-volatile memory storage components solely used to store data.
2. Microprocessor Card	Contains both volatile memory and a processing unit (microprocessor components).

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12. Bio-metric Sensor

• Definition: A type of device used to recognize and authenticate a person's fingerprints.
• Key Characteristics: It operates with exceptional accuracy and efficiency.
• Major Applications:
  • Security: Primarily used for robust security purposes.
  • Attendance Tracking: Used to record the daily attendance of employees in organizations or students in educational institutions.

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13. Scanner

• Definition: An optical input device used to convert physical data or printed images on paper into a Digital/Electronic Format.
• How it Works: It uses light as an input mechanism to convert the physical image into an electronic form, which is then sent directly to the computer.
• Main Advantage: It allows documents to be stored in their original visual form digitally, making it easy to apply modifications or edits later on.

Types of Scanners:

Hand Held Scanner

• Design: Very small in size and lightweight, allowing the user to easily hold it in their hand while scanning.
• Mechanism: If a document is large, the user must manually scan different parts of the document piece-by-piece.
• Pros: Its compact size and lightweight nature are its most significant advantages.

 

Flatbed Scanner:

• These are large, expensive, and produce very high-quality images.
• They have a flat surface where the document is placed for scanning, functioning very similarly to a photocopy machine.
• It scans one entire page at a time.

Drum Scanner:

• These are medium-sized scanners equipped with a rotating drum.
• The paper is fed into the scanner, and the drum rolls over the entire page to scan it.
• It works similarly to a fax machine.

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2. Audio and Video Input Devices

A. Microphone (Mic)

• Definition: An input device used to feed sound or voice into the computer.
• How it Works: It captures voice and converts it into a computer-readable format, creating digitized sound or digital audio.
• Hardware Requirement: Requires a Sound Card to convert the analog voice into digital format.
• Modern Application: Used extensively with Speech Recognition Software. This technology allows users to type documents simply by speaking, eliminating the need to type on a keyboard.

B. Webcam (Web Camera)

• Definition: A digital video-capturing input device connected directly to a computer.
• Primary Uses: Video conferencing, online chatting, and capturing static pictures.
• Functionality: When connected to the internet, it allows two or more people to see each other easily while communicating.

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3. Important Exam Facts (Quick Knowledge)

• Optical Mouse: Invented by Microsoft in the year 1999.
• Scanner Formats: Scanners can store images in both Gray Scale and Colour Mode.
• ICR (Intelligent Character Recognition): OCR technology was further developed to recognize characters with higher accuracy, which led to the creation of ICR.
• Speech Recognition Applications: Used in airplane cockpits, voice dialing, simple data entry, and speech-to-text processing.

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4. Output Devices

• Definition: Devices used to view or receive the processed results (output) from the computer.
• Classification of Output: Output is presented in two main forms:

Output Type	Definition	Common Examples
Soft Copy	Output that is temporary and can only be seen on a screen or heard via audio.	Monitor screen, Speaker sound.
Hard Copy	Output that is physical, permanent, and printed on paper.	Printer pages, Plotter outputs.

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5. Monitor (Visual Display Unit - VDU)

• Definition: The primary output device that displays soft copy results. It is also known as a VDU (Visual Display Unit).
• Types based on Color:
  1. Monochrome: Uses only a single color to display text/images.
  2. Color Display: Can display up to 256 colors simultaneously.
• Pixels: Images on a monitor are formed by thousands of tiny dots called Pixels.

Factors Determining Monitor Image Clarity

The visual clarity of any monitor depends heavily on three elements:

1. Screen Resolution: The mathematical product of horizontal and vertical pixels on the screen. Rule: Higher resolution = closer pixels = clearer image.
2. Dot Pitch: The diagonal distance between two colored pixels. Rule: Lower dot pitch = higher resolution = sharper image.
3. Refresh Rate: The number of times the monitor screen refreshes per second. Rule: Higher refresh rate = better and clearer picture quality.

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6. Types of Monitors

Monitor Type	Full Form	Key Features & Technology
CRT	Cathode Ray Tube	Bulky, box-like, and heavy. Uses an Electron Gun to shoot electrons onto a Phosphorus-coated screen to create glowing images.
LCD	Liquid Crystal Display	Slimmer and lighter. Contains a special Liquid trapped between two plates. Backlight aligns the liquid to form images.
LED	Light Emitting Diode	Uses tiny light-emitting diodes that glow when electricity passes through them. Initially emitted red light, now uses RGB (Red, Green, Blue) to create full-color images.
3D Monitor	Three Dimension Monitor	Displays output in three dimensions, providing highly realistic and clearer pictures compared to standard 2D monitors.
TFT / AMLCD	Thin-Film-Transistor / Active-Matrix LCD	Uses 1 to 4 transistors to control each pixel. Extremely bright, colorful, and fast. Major Pro: Pictures remain clear even when viewed from different side angles.

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7. Printers

• Definition: An output device used to print data and information onto paper, producing a Hard Copy.
• Printers can print both Black & White and Color documents.

Measurement Metrics for Printers (Highly Exam Relevant)

• Printer Speed is measured in:
  • CPS: Characters Per Second
  • LPM: Lines Per Minute
  • PPM: Pages Per Minute
• Printer Quality is measured in:
  • DPI: Dots Per Inch. (More dots per inch = significantly better print quality).

Types of Printers

Printers are broadly classified into two categories: Impact Printers and Non-Impact Printers.

1. Impact Printers

• Mechanism: Works similarly to a traditional typewriter. It uses small pins or hammers with raised letters that strike against an ink ribbon to leave a mark on the paper.
• Characteristics:
  • Prints only one character or one line at a time.
  • Produces lower-quality prints.
  • They are highly noisy during operation but are much cheaper than other modern printers.

• Key Types of Impact Printers:
  1. Dot Matrix Printer: Uses a matrix of pins to strike the ribbon, creating characters out of small dots. Also called a "Pin Printer," it prints one character at a time, is very slow, and makes a lot of noise.
  2. Daisy Wheel Printer: Prints characters like a typewriter. Provides higher resolution and more reliable output compared to dot matrix printers.
  3. Line Printer: Prints an entire line at once. While print quality is lower, its printing speed is exceptionally fast.
  4. Drum Printer: A type of line printer featuring a continuously rotating cylindrical drum with raised characters. A hammer strikes the paper and ribbon against the drum to print.

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2. Non-Impact Printers

• Mechanism: These do not physically strike the paper. Instead, they use technologies like ink spray, chemicals, or electrostatic charges to print text and images.
• Advantage: They provide much higher print quality and graphics compared to impact printers, though they are generally more expensive.

Key Types of Non-Impact Printers

• A. Inkjet Printer:
  • Sprays tiny drops of wet ink onto the paper to form characters.
  • Instead of a ribbon, it uses a Cartridge filled with wet ink (acting as the print head).
  • Typically uses two cartridges: One Black, and one Color (Magenta, Yellow, Cyan/Green-Bluish).
  • Exam Tip: It prints 1 to 4 pages per minute (ppm) and must be used frequently to prevent the ink cartridge from drying out.
• B. Thermal Printer:
  • Uses heat to melt ink onto chemically treated paper.
  • It is slower and more expensive to operate. Fax machines commonly use this technology.
• C. Laser Printer:
  • Operates similarly to a photocopy machine, providing high-quality text and graphics.
  • Uses a laser beam to create an electric charge on a drum; dry ink powder called Toner sticks to this charge and is pressed onto the paper.
  • Speed & Quality: Capable of 5 to 24 ppm with a high density of 300 to 1200 DPI.
• D. Electro Magnetic Printer:
  • A highly fast page printer that can print a whole page at once.
  • Can print up to 20,000 lines per minute or 250 pages per minute.
• E. Electro Static Printer:
  • Used mostly for large-format printing in heavy-duty printing presses because of its high speed and low operational costs.

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3. Plotters

• Definition: A specialized output device used to print large, high-quality vector graphics such as construction plans, mechanical blueprints, and CAD/CAM designs.
• Mechanism: Uses drawing tools like pens, pencils, or markers held on a moving rod to draw over a flat surface.
• Types of Plotters:
  1. Flat Bed Plotter: Smaller in size, sits on a desk, and uses a limited, fixed-size paper.
  2. Drum Plotter: Very large and uses a continuous roll of paper, allowing for unlimited paper length.

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4. Additional Output Devices

• Speakers: Converts electrical data received from the computer into sound. Crucial Fact: A computer requires a Sound Card in the CPU to generate and output this sound.
• Headphones: Functions like mini-speakers worn over the ears. Only the user can hear the output. Often comes with a microphone (headset) for two-way communication.
• Projector: A temporary output device that projects computer data onto a large screen, making it ideal for group viewings, classrooms, or conferences.

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5. Input/Output Ports (I/O Ports)

• Definition: The external physical interfaces (slots) on a computer used to connect peripheral devices like printers, modems, and joysticks.

Classification of Important Ports

Port Type	Key Features	Devices Commonly Connected
Parallel Port	Transfers 8 bits of data simultaneously via multiple wires; very fast transmission.	Printers.
Serial Port (COM)	Sends data slowly, 1 bit at a time. Also known as a Communication (COM) port.	Modems, Barcode Readers, Plotters.
USB (Universal Serial Bus)	The most common port today with "Plug and Play" features. Up to 127 devices can be connected to a single USB port.	Keyboards, Mice, Modern Printers, Flash Drives.
Fire Wire	High-speed, expensive technology for massive data transfer (up to 400 MB/sec).	Video Cameras, Hard Disk Drives, DVD Drives.

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6. Important Exam Facts (Miscellaneous)

• Modem: An essential device used to both receive and transmit data over networks.
• Standard Devices: The foundational devices required to operate a computer (e.g., Keyboard, Hard Disk).
• Refresh Rate: A monitor's refresh rate is always measured in Hertz (Hz).
• Magnetic Interference: Strong magnetic fields can turn a monitor screen black or distort colors, acting almost like a virus. Always keep magnets away from monitors.
• Graphic Display Unit: Modern monitors are highly capable of displaying both alphanumeric characters as well as complex graphs and diagrams.

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Quick Revision Summary (Key Takeaways)

• Peripheral Devices: The collective name for all I/O devices attached to a computer.
• Input Device Role: Acts as a translator converting Human Data $\rightarrow$ Machine Language for the CPU.
• Keyboard Processing: Key pressed $\rightarrow$ Keyboard Controller $\rightarrow$ Keyboard Buffer $\rightarrow$ CPU $\rightarrow$ Output Device.
• Keyboard Types: QWERTY, DVORAK, AZERTY.
• Function Keys: F1 to F12, located at the top, used for specific programmed commands.
• Arrow Keys Layout: Arranged in an inverted 'T' shape.
• Navigation Shortcuts: Home (start of line/doc), End (end of line), Page Up (previous page), Page Down (next page).
• Control Keys: Used in combinations (like Ctrl + S) to execute special commands.
• Enter Key = Execution key / "OK" alternative.
• Esc Key = Cancels tasks. Ctrl + Esc = Start Menu.
• Shift + Delete = Permanently deletes a file.
• Spacebar = Longest key on the keyboard.
• Tab Key = Jumps 5 spaces forward.
• Toggle Keys = Caps Lock & Num Lock (change states On/Off).
• Standard QWERTY Keyboard = 104 keys.
• Pointing Devices = Mouse, Trackball, Joystick, Light Pen, Touch Screen.
• Mouse Inventor = Douglas C. Engelbart (1963).
• Left Click = Selects objects; Double Click = Opens programs.
• Right-Click: Used to access object properties.
• Drag & Drop: Moves items across the screen.
• Trackball: A stationary mouse alternative with a rolling ball on top; used in CAD, CAM, and radar systems.
• Joystick: Handle-based pointing device ideal for gaming and flight simulators. Unlike a mouse, the pointer moves continuously in the pointed direction.
• Light Pen: Electro-optical device with a photocell used for direct on-screen drawing; popular in PDAs.
• Touch Screen: Takes direct finger input; used in ATMs, mobiles, and kiosks.
• Graphic Tablets: Converts hand-drawn art into digital signals for artists.
• Bar Code Reader: Uses a light beam and light-sensitive detector to read vertical ink lines (Universal Product Code) and converts them into numeric codes. Mostly used in supermarkets.
• OMR (Optical Mark Reader): Uses light to read marks on paper; mainly used for checking objective exam sheets.
• OCR (Optical Character Recognition): Reads printed/handwritten letters by shape using light; speed is 1500–3000 characters/second. Used for bills and old docs.
• MICR (Magnetic Ink Character Reader): Reads special ink containing iron particles. Exclusively used by banks for cheque processing.
• Smart Card Reader: Accesses microprocessors in plastic security cards (Memory Cards or Microprocessor Cards).
• Bio-metric Sensor: Highly accurate device used for fingerprint scanning, attendance, and security.
• Scanner: Converts hard-copy papers and images into digital/electronic formats using light.
• Hand Held Scanner: A small, portable scanner that requires manual swiping over different parts of a document.
• Microphone & Sound Card: A mic captures voice; a sound card digitizes it.
• Soft Copy vs Hard Copy: Soft copy = Screen/Audio (Monitor). Hard copy = Physical paper (Printer).
• Pixels & Clarity: Images are made of pixels. Image clarity relies on Resolution, Dot Pitch (lower is better), and Refresh Rate (higher is better).
• CRT vs LCD vs LED vs TFT:
  • CRT: Heavy, uses an electron gun & phosphorus.
  • LCD: Uses illuminated liquid between plates.
  • LED: Uses light-emitting diodes (RGB).
  • TFT: Uses transistors for each pixel, offers the best viewing angles.
• Printer Speed Units: CPS, LPM, PPM.
• Printer Quality Unit: DPI (Dots Per Inch).
• Impact Printers: Strike an ink ribbon directly onto paper (like typewriters). Noisy, cheap, low quality.
• Dot Matrix Printer: Uses pins and a ribbon; very slow, noisy, prints in dots.
• Line vs. Page Printers: Line printers (Drum/Line) print a whole line at once; Page printers (Laser/Electromagnetic) print a full page at once.
• Inkjet vs. Laser: Inkjet uses liquid ink cartridges; Laser uses dry powder toner and electrostatic charges.
• Plotter Application: Best for CAD/CAM, engineering blueprints, and very large architectural designs.
• Sound Card Requirement: Essential for speakers to convert electrical data into audio.
• Parallel vs. Serial Ports: Parallel transfers 8 bits at once (fast, used for printers); Serial transfers 1 bit at a time (slow, used for modems).
• USB Port Capacity: A single USB controller can theoretically support up to 127 connected devices.
• FireWire: Built for high-speed multimedia data transfer (400 MB/s).