Input devices

Input devices

An input unit of a computer system performs the following functions:

  • It accepts (or reads) instructions and data from outside world
  • It converts these instructions and data in computer acceptable form
  • It supplies the converted instructions and data to the computer system for further processing
  • Provide means of communication between a computer and outer world
  • Also known as peripheral devices because they surround the CPU and memory of a computer system
  • Input devices are used to enter data from the outside world into primary storage
  • Output devices supply results of processing from primary storage to users
Role of I/O Devices

Commonly Used Input Devices

  • Keyboard devices
  • Point-and-draw devices
  • Data scanning devices
  • Digitizer
  • Electronic cards based devices
  • Speech recognition devices
  • Vision based devices

Keyboard Devices

  • Allow data entry into a computer system by pressing a set of keys (labeled buttons) neatly mounted on a keyboard connected to a computer system
  • 101-keys QWERTY keyboard is most popular

Point-and-Draw Devices

  • Used to rapidly point to and select a graphic icon or menu item from multiple options displayed on the Graphical User Interface (GUI) of a screen
  • Used to create graphic elements on the screen such as lines, curves, and freehand shapes
  • Some commonly used point-and-draw devices are mouse, track ball, joy stick, light pen, and touch screen


  • Commonly used in personal computers and workstations


  • Commonly used in laptop (notebook) computers


Commonly used for video games, flight simulators, training simulators, and for controlling industrial robots

Electronic Pen

  • Pen-based point-and-draw device
  • Used to directly point with it on the screen to select menu items or icons or directly draw graphics on the screen
  • Can write with it on a special pad for direct input of written information to a system
  • Pressure on tip of a side button is used to cause same action as right-button-click of a mouse

Touch Screen

  • Most simple, intuitive, and easiest to learn of all input devices
  • Enables users to choose from available options by simply touching with their finger the desired icon or menu item displayed on the screen
  • Most preferred human-computer interface used in information kiosks (unattended interactive information systems such as automatic teller machine or ATM)

Data Scanning Devices

  • Input devices that enable direct data entry into a computer system from source documents
  • Eliminate the need to key in text data into the computer
  • Due to reduced human effort in data entry, they improve data accuracy and also increase the timeliness of the information processed
  • Demand high quality of input documents
  • Some data scanning devices are also capable of recognizing marks or characters
  • Form design and ink specification usually becomes more critical for accuracy

Image Scanner

  • Input device that translates paper documents into an electronic format for storage in a computer
  • Electronic format of a scanned image is its bit map representation
  • Stored image can be altered or manipulated with an image-processing software

Optical Character Recognition (OCR) Device

  • Scanner equipped with a character recognition software (called OCR software) that converts the bit map images of characters to equivalent ASCII codes
  • Enables word processing of input text and also requires less storage for storing the document as text rather than an image
  • OCR software is extremely complex because it is difficult to make a computer recognize an unlimited number of typefaces and fonts
  • Two standard OCR fonts are OCR-A (American standard) and OCR-B (European standard)

Optical Mark Reader (OMR)

  • Scanner capable of recognizing a pre-specified type of mark by pencil or pen
  • Very useful for grading tests with objective type questions, or for any input data that is of a choice or selection nature
  • Technique used for recognition of marks involves focusing a light on the page being scanned and detecting the reflected light pattern from the marks
Bar-code Reader

  • Scanner used for reading (decoding) bar-coded data
  • Bar codes represent alphanumeric data by a combination of adjacent vertical lines (bars) by varying their width and the spacing between them
  • Scanner uses laser-beam to stroke across pattern of bar code. Different patterns of bars reflect the beam in different ways sensed by a light-sensitive detector
  • Universal Product Code (UPC) is the most widely known bar coding system

Magnetic-Ink Character Recognition (MICR)

  • MICR is used by banking industry for faster processing of large volume of cheques
  • Bank’s identification code (name, branch, etc.), account number and cheque number are pre-printed (encoded) using characters from a special character set on all cheques
  • Special ink is used that contains magnetizable particles of iron oxide
  • MICR reader-sorter reads data on cheques and sorts them for distribution to other banks or for further processing


  • Input device used for converting (digitizing) pictures, maps and drawings into digital form for storage in computers
  • Commonly used in the area of Computer Aided Design (CAD) by architects and engineers to design cars, buildings medical devices, robots, mechanical parts, etc.
  • Used in the area of Geographical Information System (GIS) for digitizing maps available in paper form

Electronic-card Reader

  • Electronic cards are small plastic cards having encoded data appropriate for the application for which they are used
  • Electronic-card reader (normally connected to a computer) is used to read data encoded on an electronic card and transfer it to the computer for further processing
  • Used together as a means of direct data entry into a computer system
  • Used by banks for use in automatic teller machines (ATMs) and by organizations for controlling access of employees to physically secured areas

Speech Recognition Devices

  • Input device that allows a person to input data to a computer system by speaking to it
  • Today’s speech recognition systems are limited to accepting few words within a relatively small domain and can be used to enter only limited kinds and quantities of data

Vision-Input Systems

  • Allow computer to accept input just by seeing an object.
  • Input data is normally an object’s shape and features in the form of an image
  • Mainly used today in factories for designing industrial robots that are used for quality-control and assembly processes

Qus. What is volatile memory?

Ans: RAM is known as Volatile Memory because when we switch off the computer its data is vanished.

Qus. Define each of the following:

(a) byte (b) kilobyte (c) megabyte (d) gigabyte (e) terabyte


(a) byte: This is the unit of memory in computer. 1 byte = 8 bits

(b) kilobyte: This is the unit of memory in computer. 1 kilobyte = 1024 bytes

(c) megabyte: This is the unit of memory in computer. 1 megabyte = 1024 kilobytes

(d) gigabyte: This is the unit of memory in computer. 1 gigabyte = 1024 megabytes

(e) terabyte: This is the unit of memory in computer. 1 terabyte = 1024 gigabytes.

Qus. State the basic units of computer. Name the subunits that make up the CPU, and give the function of each of the unit.

Ans: Basic units of computer are Input Unit, Central Processing Unit and Output Unit. Sub unites of CPU are Arithmetical Logical Unit(ALU), Control Unit (CU) and Memory Unit(MU).

Qus. What is the function of memory? What are its measuring units?

Ans: The computer memory is a temporary storage area. It holds the data and instructions that the Central Processing Unit (CPU) needs. Before a program can run, the program is loaded from some storage medium into the memory. This allows the CPU direct access to the program. Its measuring units are byte, kilobyte, megabyte, gigabyte, terabyte etc.

Qus. Why is primary memory termed as „destructive write‟ memory but „non-destructive read‟ memory?

Ans: The primary memory is called destructive write because the data enter here are temporary. That‘s why your RAM gets cleared after every restart.

Qus. What is the role of CPU of a mobile system?

Ans: A mobile processor is found in mobile computers and cellphones. A CPU chip is designed for portable computers, it is typically housed in a smaller chip package, but more importantly, in order to run cooler, it uses lower voltages than its desktop counterpart and has more sleep mode capability. A mobile processor can be throttled down to different power levels or sections of the chip can be turned off entirely when not in use. Further, the clock frequency may be stepped down under low processor loads. This stepping down conserves power and prolongs battery life.

Qus. What is SoC? how it is different from CPU? Why is it considered a better development?

Ans: A system on a chip (SoC) combines the required electronic circuits of various computer components onto a single, integrated chip (IC). SoC is a complete electronic substrate system that may contain analog, digital, mixed-signal or radio frequency functions. Its components usually include a graphical processing unit (GPU), a central processing unit (CPU) that may be multi-core, and system memory (RAM). Because SOC includes both the hardware and software, it uses less power, has better performance, requires less space and is more reliable than multi-chip systems. Most system-on-chips today come inside mobile devices like smartphones and tablets.

Qus. Briefly explain the basic architecture of a computer.

Ans: Computer organization refers to logical structure of a computer describing how its components are connected to one another, how they affect one another‘s functioning and contributes to overall performance of computer.

Computers follow the 'IPO' principal i.e. Input ->Process -> Output

(That means a certain input is processed to Generate specific output)

Qus. What do you understand by input unit? What is its significance? What does computer system consist of?

Ans: Input unit is formed by the input devices(Keyboard, mouse, MICR, OBCR etc.) attached to the computer. Input unit is responsible for taking input and converting it into computer understandable form(the binary code). Some common input devices are:

(i) Keyboard

(ii) Mouse

(iii) Microphone

(iv) Scanner

(v) Webcam

(vi) Optical Bar Code Reader

(vii) Optical Mark Reader

(viii) Magnetic Ink Character Reader

(ix) Touch Pad

(x) Track Ball

(xi) Joy stick

(xii) Touch Screen

(xiii) Biometric Sensors. Etc.

Qus. What is the function of CPU in a computer system? What are its sub units?

Ans: The central processing unit (CPU) of a computer is a piece of hardware that carries out the instructions of a computer program. It performs the basic arithmetical, logical, and input/output operations of a computer system. The CPU is like the brains of the computer - every instruction, no matter how simple, has to go through the CPU. So let's say you press the letter 'k' on your keyboard and it appears on the screen - the CPU of your computer is what makes this possible. The CPU is sometimes also referred to as the central processor unit, or processor for short. So when you are looking at the specifications of a computer at your local electronics store, it typically refers to the CPU as the processor. Its sub units are:

(i) Control Unit (ii) Arithmetical and Logical Unit (ALU) (iii) Memory Unit

Qus. What functions are performed by the control unit?

Ans: The CU controls and guides the interpretation, flow and manipulation of all data and information. CU sends control signals until the required operations are done properly by ALU and memory. Another function of CU is the program execution. It means carrying out all the instructions stored in the program. CU gets program instruction from the memory and executes them one after the other. CU acts as a supervisor by controlling and guiding the operation taking place.

Qus. Distinguish between CPU and ALU?

Ans: Difference Between ALU and CPU is that arithmetic logic unit (ALU), another component of the processor, performs arithmetic, comparison, and other operations. While Processor also central processing unit (CPU), interprets and carries out the basic instructions that operate a computer.

The main difference between CPU and ALU is that the CPU is an electronic circuit that handles instructions to operate the computer while the ALU is a subsystem of the CPU that performs arithmetic and logical operations.

Qus. What is the function of output unit in a computer

Ans: Input devices are the hardware that give computers instructions. Output devices relay the response from the computer in the form of a visual response (monitor), sound (speakers) or media devices (CD or DVD drives). The purpose of these devices is to translate the machine's response to a usable form for the computer user.

Qus. Distinguish between internal and external memory.

Ans: Internal memory is usually chips or modules that you attach directly to the motherboard. Internal Memory is a circular disc that continuously rotates as the computer accesses its data. External memory often comes in the form of USB flash drives; CD, DVD, and other optical discs; and portable hard drives.

Qus. What are RAM and ROM? How are they alike? How are they different? What are PROM, EPROM, EEPROM?

Ans: A ROM chip is a non-volatile storage medium, which means it does not require a constant source of power to retain the information stored on it.

A RAM chip is volatile, which means it loses any information it is holding when the power is turned off.

Both of them are known as primary memory as they can directly work with CPU.

Read Only Memory (ROM)

Programmable Read Only Memory (PROM)

Erasable Programmable Read Only Memory (EPROM)

Electrically Erasable Programmable Read Only Memory (EEPROM)

Qus. What are major functional components of a mobile system?

Ans: Major functional components of a mobile system are-

(i) Mobile Processor

a. Communications Processing Unit

b. Application Processing Unit

c. GPU (Graphics Processing Unit)

(ii) SoC (System on a chip)

(iii) Display Subsystem

a. Display Screen

b. Touch Sensitive Interface

c. Touch Sensitive Keyboards

(iv) Camera Subsystem

(v) Mobile System Memory

a. RAM

b. ROM

(vi) Storage

(vii) Power Management Subsystem

Qus. Draw a block diagram depicting organization of a mobile system.

Qus. What is the role of Power Management Unit in a mobile system?

Ans: This subsystem is responsible for providing power to a mobile system. The mobile systems work on limited power provided through an attached battery unit. This system has a battery management system that works with a battery charger and a battery unit and provides power to the mobile system in required form.

It also contains a collection of different functions like battery charging, monitoring and supplying many different voltages these systems require. It also contains software controlled turn-on and turn-off feature to optimize the power consumption and battery life.

Qus. What does the communication processor do?

Ans: this subsystem is responsible for making and receiving phone calls on a mobile handset. It has a digital signal processor that helps it work with RF Transceiver and the Audio subsystem.

Qus. What is GPU? How is it useful?

Ans: Graphics Processing Unit assists the CPU by handling the visuals, other graphically-rich applications. In short, GPU handles all graphics-related chores of a mobile CPU.


CCC Online Test 2021 CCC Practice Test Hindi Python Programming Tutorials Best Computer Training Institute in Prayagraj (Allahabad) Best Java Training Institute in Prayagraj (Allahabad) Best Python Training Institute in Prayagraj (Allahabad) O Level NIELIT Study material and Quiz Bank SSC Railway TET UPTET Question Bank career counselling in allahabad Sarkari Naukari Notification Best Website and Software Company in Allahabad Website development Company in Allahabad