Output devices

Output Devices

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

  • It accepts the results produced by the computer, which are in coded form and hence, cannot be easily understood by us
  • It converts these coded results to human acceptable (readable) form
  • It supplies the converted results to outside world

Commonly Used Output Devices

  • Monitors
  • Printers
  • Plotters
  • Screen image projector
  • Voice response systems

Types of Output

Soft-copy output

  • Not produced on a paper or some material that can be touched and carried for being shown to others
  • Temporary in nature and vanish after use
  • Examples are output displayed on a terminal screen or spoken out by a voice response system

Hard-copy output

  • Produced on a paper or some material that can be touched and carried for being shown to others
  • Permanent in nature and can be kept in paper files or can be looked at a later time when the person is not using the computer
  • Examples are output produced by printers or plotters on paper


  • Monitors are the most popular output devices used for producing soft-copy output
  • Display the output on a television like screen
  • Monitor associated with a keyboard is called a video display terminal (VDT).
  • It is the most popular Output device

Types of Monitors

  • Cathode-ray-tube (CRT) monitors look like a television and are normally used with non-portable computer systems
  • Flat-panel monitors are thinner and lighter and are commonly used with portable computer systems like notebook computers. Now they are also used with non- portable desktop computer systems because they occupy less table space.


Most common output devices for producing hard-copy output

Dot-Matrix Printers

  • Character printers that form characters and all kinds of images as a pattern of dots
  • Print many special characters, different sizes of print and graphics such as charts and graphs
  • Impact printers can be used for generating multiple copies by using carbon paper or its equivalent
  • Slow, with speeds usually ranging between 30 to 600 characters per second
  • Cheap in both initial cost and cost of operation

Inkjet Printers

  • Character printers that form characters and all kinds of images by spraying small drops of ink on to the paper
  • Print head contains up to 64 tiny nozzles that can be selectively heated up in a few micro seconds by an integrated circuit register
  • To print a character, the printer selectively heats the appropriate set of nozzles as the print head moves horizontally
  • Can print many special characters, different sizes of print, and graphics such as charts and graphs
  • Non-impact printers. Hence, they cannot produce multiple copies of a document in a single printing
  • Can be both monochrome and color
  • Slower than dot-matrix printers with speeds usually ranging between 40 to 300 characters per second
  • More expensive than a dot-matrix printer

Laser Printers

  • Page printers that print one page at a time
  • Consist of a laser beam source, a multi-sided mirror, a photoconductive drum and toner (tiny particles of oppositely charged ink)
  • To print a page, the laser beam is focused on the electro statically charged drum by the spinning multi-sided mirror
  • Toner sticks to the drum in the places the laser beam has charged the drum’s surface.
  • Toner is then permanently fused on the paper with heat and pressure to generate the printer output
  • Laser printers produce very high quality output having resolutions in the range of 600 to 1200 dpi


Plotters are an ideal output device for architects, engineers, city planners, and others who need to routinely generate high-precision, hard-copy graphic output of widely varying sizes

Two commonly used types of plotters are:

  • Drum plotter, in which the paper on which the design has to be made is placed over a drum that can rotate in both clockwise and anti-clockwise directions
  • Flatbed plotter, in which the paper on which the design has to be made is spread and fixed over a rectangular flatbed table

Screen Image Projector

  • An output device that can be directly plugged to a computer system for projecting information from a computer on to a large screen
  • Useful for making presentations to a group of people with direct use of a computer
  • Full-fledged multimedia presentation with audio, video, image, and animation can be prepared and made using this facility

Voice Response Systems

  • Voice response system enables a computer to talk to a user
  • Has an audio-response device that produces audio output
  • Such systems are of two types:
  • Voice reproduction systems
  • Speech synthesizers

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.


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