Input And Output Devices

Introduction

Input-Output devices are very important component of computer system. Here we will discuss about Input-Output devices of computer system. First, we will discuss briefly about Input-Output devices and then move on to the function and structure of some Input and Output devices and we will discuss about the newer technologies in Input-Output devices used in computer system.

 

Input-Output Devices

The computer will be of no use if it is not communicating with the external world. Thus, a computer must have a system to receive information from the outside world and must be able to communicate results to the external world. For this purpose computers use Input-Output devices. Input and Output devices can also be written as I/O devices.

Input and Output devices of a computer system are the devices that connect you to computer. Input devices let you to transfer data and user commands into the computer. Input devices technologies are rapidly developing and are used to interact with the computer system. For example, you can type in data by using a keyboard, or you can input data in picture form by using a scanner in computer system. Inputs are data or signals received by the computer system and outputs are the data and signals which are sent by it as a result of processing the input.

The output devices display the result of input data or signals after processing it. Examples of these could be your computer’s monitor, which displays all the programs which are running into the computer, as well as the printer, which will print out a hard copy of the information that is saved on your computer.

Input and Output devices allow the computer system to interact with the outside world by moving data into and out of the system. An Input device is used to bring data into the system. And an output device is used to send data out of the system.

Examples Of Some Input Devices

• • Keyboard
  • Mouse
  • Joy­stick
  • Microphone
  • Bar Code Reader
  • Graphics Tablet

Examples Of Some Output Devices

• • Monitor
  • Printer
  • Plotter
  • Speaker

Input and Output devices in short are also called I/O devices. They are directly connected to an electronic module called the I/O module or device controller. For example, the speakers of a multimedia computer system are directly connected to a device controller called an audio card which in turn is connected to the rest of the system.

Input and Output devices are similar in operation but perform opposite functions. It is through the use of these devices that the computer is able to communicate with the outside world.

Input Data For The Computer System Can Be In Any Of The Following Forms:

• • Manual inputs from a keyboard or console.
  • Analog inputs from instruments or sensors.
  • Inputs from a storage device, such as Pen­-Drive, CD’s, and Floppy Drives.

The speed of the processor is more than the input devices, such as keyboard of computer system. Computer system can process hundreds or thousands of characters per second. Thus, a study of the first method i.e., manual input reflects the inability of human-operated keyboards or keypunches to supply data at a speed that matches the speed of digital computers.

 

• Monitors

One of the most important output devices in computer system is its screen commonly called monitor. It is an output device and displays all the programs and applications to which you are running in your computer system. Monitor is the visual display unit of the computer system. It displays images generated from the video output. Monitor of the computer system is used to display images without keeping a permanent record inside it.

Graphic display is made up of a series of dots called ‘pixels’ [picture elements] whose pattern produces images in computer system. Each dot on the screen is defined as a separate unit which can be addressed separately. Since each dot on the screen can be controlled separately by virtue of which it gives greater flexibility in drawing pictures. Number of dots per inch [dpi] is called the resolution of the screen and is used to represent the quality of the computer system.

There Are Three Categories Of Display Screen Technology:

1. 1. Normal Cathode Ray Tube [CRT].
   2. Liquid Crystal Display [(LCD)/(TFT LCD)].
   3. Projection Displays.

Normal Cathode Ray Tube Monitors [CRT]

Monitors display what is going on in your computer. They can run at various resolutions. It is the part of the computer which looks like a TV set. After typing the characters from the keyboard we can see them on the monitor.

The main components of a CRT monitors are the electron gun, the electron beam controlled by an electromagnetic field, and the phosphor coated display screen. These older monitors were very bulky and acquire a lot of space for installation.

In CRT monitors image is projected on the screen by directing the electron beam on the computer screen. To precisely direct the electron beams, copper steering coils are used to create magnetic field inside the tube. By applying a varying voltage to copper coils a beam can be positioned at any point on the screen.

Liquid Crystal Displays [LCD]

This was first introduced in watches and clocks in 1970s. LCD is now used to display images in monitors. A newer technology in computer screens is TFT LCD monitors. These are light weight monitors and are used in laptop computers.

The three main advantages of these monitors over the CRT are the use of less space on the desk, less power consumption, and a flicker free screen.

These monitors are portable and consume less electricity. Images produced by these monitors are of better quality than that of old CRT monitors. The LCD monitors have very high resolution and emit less radiation than CRT monitors.

Projection Displays

These are normally used for large group presentations. These systems can be connected to computer and whatever appears on the computer terminal gets enlarged and projected on a large screen. In this computers are connected to an LCD Flat screen and images are projected on a large screen by using overhead projector. These are popularly used for seminars, classrooms, marketing presentations, etc.

Classification Of Monitors On The Basis Of Color

Monochrome: These monitors display the result in two colors, i.e., black/white, green/black, amber/black. One color is for background of the screen and other for the foreground and you may see it being used at railway reservation counters.

Gray Scale: It is monochrome type of the monitor, but it displays the output by using the different shades of gray, made by combination of black and white.

Color Monitor: It can display the output in many colors, ranging from 16 to over 1 million different colors. These are also called as RGB monitors, because they accept three separate signals, which are red, green, and blue.

Classification Of Monitors On The Basis Of Size

After color classification, the most important aspect of a monitor is its screen size. Size of computer screen is measured in diagonal inches and is given by measuring the distance from one corner to the opposite corner [diagonally]. The smallest size for VGA monitors is 14 inches, which is also the entry level monitor for the computer system. The larger size landscape monitors can display two full pages side by side at a time.

Classification Of Monitors On The Basis Of Resolution

The resolution of a monitor means number of pixels per inch are of the monitor. In general, the number of more pixels will be the sharper images. Most modern monitors can display 1024 by 768 pixels. Some high­-end models of computer monitors can display 1280 by 1024, or even 1600 by 1200 pixels.

Classification Of Monitors On The Basis Of Signal

Analog Monitor: Electronic signal that is sent by signals of varying frequency instead of sent as ON or OFF data transmission is called analog signal. Analog allows equipment to handle information that continuously changes such as voltage, current, wave, etc. Analog signals can be represented by wave sign and watches which changes their position continuously. These are traditional types of color monitors which are based on CRT technology. These work like the television screen and accept analog signals.

Digital Monitor: An electronic signal that is sent as binary digits of either ON or OFF is called Digital signal. The digital monitor receives digital signals and uses CRT technology. The data in these monitors is received from a video adapter. These are of different types such as CGA [Color Graphics Adapter], EGA [Enhanced Graphics Adapter], VGA [Video Graphics Array], SVGA [Super Video Graphics Array], and are fast and produce clear images.

 

• Printers

Printers are used for producing output on paper. There are a large variety of printers and printing devices. These devices can be classified according to the print quality and printing speed.

There are vast varieties of printers. Classification of these printers can be done by the technology used by them. These varieties of printers are:

Printing Technology: Impact Printers Vs. Non-Impact Printers

Impact printers use variations of standards typewriter printing mechanism where a hammer strikes the paper through an inked ribbon. A non-­impact printer uses chemical, heat, or electrical signals to each or induces symbols on paper. Many of these require specially coated or treated paper to print characters on them.

Classification Of Printers On The Basis Of Speed

1- Character Printer: These printers can print only one character at a time. They work similarly to that of the typewriter. The examples are Daisy Wheel Printer, Dot Matrix Printer, and Inkjet Printer.

Daisy­-Wheel Printer: This printer is similar to a ball-head typewriter. This type of printer has a plastic or metal wheel on which the shape of each character is embossed. A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper. Daisy-Wheel Printers produce letter­-quality print but cannot print graphics. The print quality of this impact printer is very low.

Dot-­Matrix Printer: This is one of the most popular printers used for personal computing systems. These printers are relatively cheaper compared to other technologies and use impact technology. In the year, 1970s and 1980s, dot matrix impact printers were generally considered the best combination of expense and versatility, and until the 1990s they were by far the most common form of printer used with personal computers. Characters in this printer are formed by a combination of dots. Dot-­Matrix printer creates characters by striking pins against an ink soaked ribbon. Each pin makes a dot and combinations of dots form characters and illustrations. The moving portion of the printer is called the print head of Dot matrix printer.

Advantage:
1- Dot Matrix Printers, like any impact printer, can print on multi­-part stationery or make carbon copies.
2- Impact printers have one of the lowest printing costs per page. As the ink is running out, the printout gradually fades rather than suddenly stopping partway through a job.
3- They are able to use continuous paper rather than requiring individual sheets, making them useful for data logging. They are good, reliable, and ideal for use in situations where printed content is more important than quality.

Disadvantages:
1- Impact printers are usually noisy.
2- They can only print low resolution graphics, with limited color performance, and limited quality.
3- Per minute page printing is low.

2- Line Printer: Line printers are used to print large amount of data. These are fast speed printers ranging from 300 to 2500 lines per minute. Examples are Drum Printers and Chain Printers.

3- Page Printer: These are very high-speed printers which produce high-quality output. Their speed ranges from 10­-25 pages per minute. These printers use modern Laser Printer technology and print whole page at one go. There are many varieties of laser page printers and so their prices from base label to high label.

Classification Of Printers On The Basis Of Quality

1- Ink­-Jet Printer: The Inkjet printer works on inkjet technology and produces better quality print than dot matrix printers. These print by spraying a controlled stream of tiny oink droplets accurately on the paper forming either dot matrix or solid characters. The printing quality of this printer is very good with a speed of 700 or more characters per second. These are non-impact and hence are relatively less noise during the printing process. This printer can be used to print in color and is easy to use.

Advantages:
1- They are quieter in operation than impact printers.
2- They can print finer, smoother details through higher print head resolution.
3- It can produce photographic­-quality printing.

Disadvantages:
1- The ink is often very expensive.
2- Many intelligent ink cartridges contain a microchip that communicates the estimated ink level to the printer; this may cause the printer to display an error message, or incorrectly inform the user that the ink cartridge is empty.
3- The very narrow inkjet nozzles are prone to clogging due to dried ink.

2- Laser Printer: This is a high-quality, high-speed, and high-volume technology printer. In laser printers, a laser beam is used to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. Laser printers produce very high quality text and graphics but are very expensive. The technology used by them is the same as that of photo­copy machines. Speeds of laser printers can range from 10 pages per minute to 200 pages per minute. Laser printers are also called page printers because they print the whole page in one go.

Standard Laser Printers Can Be Classified Into Two Categories In Terms Of Color:

1. 1. Monochrome Laser Printer.
   2. Color Laser Printer.

Monochrome laser printers use a single toner. Color laser printers use four toners to print in full color. These printers are about five to ten times as expensive as their monochrome siblings.

 

• Scanners

Scanner is an input device and is used to input data into the computer system in the form of pictures. It optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Examples of scanners are desktop or flatbed scanners. In these scanners, the document is placed on a glass window for scanning. Mechanically driven scanners that move the document are typically used for a large-formatted volume of documents.

Other types of scanner are planetary scanner. This scanner takes photographs of books and documents. Three dimensional scanners are used for producing three dimensional models of objects.

 

• Diskettes

Floppy disk is a convenient data recording medium. It is called floppy because it flops if you wave it [at least, the 5¼­ inch variety does]. Floppy disks are portable and can be removed from the system. Disk drives for floppy disks are called floppy drives. Data stored in Floppy Disks are slower to access than that of hard disks. But it is less expensive than the hard disk.

Floppy Disks Come Into Three Sizes:

1. 1. 8 Inches Floppy Disk.
   2. 5.25 Inches Floppy Disk.
   3. 3.5 Inches Floppy Disk.

The earliest floppy disks, invented at IBM company, were of 8 inches in diameter. They became commercially available in 1971. Floppy disks of today are available in two sizes 5.25 inches and 3.5 inches and their storage capacity ranges from 360 KB to 1.44 MB.

Floppy disks were very popular and have been seen by all computer professionals. This is the reason why the floppy disk symbol is often seen in programs on buttons and other user interface elements related to saving of files. Now pen drive has replaced floppy disks and floppy disks are outdated.

Note:- Floppy Disks were used by computer professionals from the year 1971 to the year 2005 and are out dated now a days. Now pen drives have replaced floppy disks and are being used by the users.

Hard Disk Drive [HDD]

The Hard Disk Drive in the computer system is the data center of the computer. All the programs and data of computers are stored in it. It is the most important permanent storage device for computers. Hard disk differs from the other data storage devices, in three ways:

1. 1. Size [Usually Larger]
   2. Speed [Usually Faster]
   3. Permanence [Usually Fixed In The PC And Not Removable]

The first PC hard disks had a capacity of 10 megabytes and its cost was very high. The Modern hard disks have capacities of more than 500 gigabytes and are very cheap than to previous hard disks.

Features Of HDD: Some Of Main Features Of Hard Disk Are:

Performance: The hard disk plays a very important role in overall system performance. The speed at which the PC boots up and programs load is directly related to the hard disk speed.

Storage Capacity: Hard disks have a very high storage capacity such as 500 GB and even more. Bigger hard disk lets you store more programs and data in it.

Software Support: Newer software needs more space and faster hard disks to load it efficiently. This is supported by the present age high speed hard disk drives.

Random Access Memory [RAM]

Random Access Memory [RAM] of a computer system is a type of computer data storage device. It works similar to integrated circuits and allows the stored data to be accessed in any order, i.e. at random. The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location.

The RAM is a volatile memory i.e., the data or information saved in this memory gets lost if power is switched off. It is permanently fixed inside the computer system. Computer RAM comes in many sizes such as 256 MB, 512 MB, 1 GB, 2GB, etc. Normal PC RAM’s and Laptop RAM’s are different in size and shape.

Pen Drive

A USB flash drive is a flash memory data storage device integrated with a USB [Universal Serial Bus] interface. USB flash drives are typically removable and rewritable, much shorter than a floppy disk. Nothing actually moves in a flash drive: it is called a drive because it is designed to read and write data using the same system commands as a mechanical hard disk drive.

A flash drive is consist of a small printed circuit board protected inside a plastic, metal, or rubberized case, robust enough to be carried with no additional protection, in a pocket or on a key chain. To access the drive it must be connected to a USB port, which powers the drive and allows it to send and receive data.

USB flash drive offers potential advantage over other portable storage devices. They are more compact, faster, hold much more data, have a more durable design, and are more reliable for lack of moving parts. Pen Drive comes in various sizes such as: 256 MB, 512 MB, 1 GB, 2 GB, 4 GB, & 8 GB.

Compact Disk [CD]

The CD-ROM [Compact Disk Read-Only Memory] is a direct extension of audio CD. The CDs are available in the market since late 1982. Standard CDs have a diameter of 120 mm and can hold up to 80 minutes of audio. There are mini CDs with diameters ranging from 60 to 80 mm.

The amount of information that can be written on a CD is determined by the disc recording capacity as well as the physical and logical formats used. There are various versions of CD such as CD­-R [CD Readable], CD­-RW [CD Read­-Write], SACD [Super Audio CD], VCD [Video Compact Disk], and DVD [Digital Versatile Disk].

 

• Keyboard

It is the most common input device used for the input of data and information into the computer system. On a keyboard, alphabets are printed on the keys. The first keyboard was developed in the 1800 century and was named as QWERTY Keyboard. The standard layout of letters, numbers, and punctuation is known as a QWERTY Keyboard because the first six keys on the top row of letters spell QWERTY.

In General, A Computer Keyboard Has The Following key:

• • Alphanumeric Keys: It includes letters and numbers.
  • Punctuation Keys: These include the comma, period, semicolon, etc.
  • Special Keys: These can be, function keys, control keys, arrow keys, and caps lock keys, etc.

All The Modern Keyboards Of Computer Are Classified As:

1. 1. Original PC keyboard having 84 keys.
   2. Advanced Technology (AT) Keyboard having 101­-104 keys.
   3. Multimedia Keyboard having 120-140 keys.

 

• Mouse

Mouse is a handy device that can be moved on a smooth surface to simulate the movement of the cursor on the screen. It is a pointing device that is used to input data into computer by pointing on it. Physically, a mouse contains a small case, held under one of the user’s hands with one or more buttons. Its name is derived from its shape, which looks a bit like a mouse, its connecting wire that one can imagine to be the mouse’s tail.

Mouse Could Be Mechanical, Optical, Or Cordless Types:

Mechanical Mouse: Mechanical Mouse uses ball for the movement of cursor on the computer screen.

Optical Mouse: Optical Mouse uses Laser rays for the movement of cursor on the computer screen.

Cord-­Less Mouse: Cord-­Less Mouse is battery-driven and does not need any wire for the physical connection with motherboard.

Computer mouse is very useful in designing pictures and graphs by multimedia designers. Mouse pad is required to move the mouse because it provides a smooth surface.

 

• Graphics Tablet

Graphics tablet is a computer input device which allows one to hand-­draw images and graphics, similar to the way one draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures. Some tablets are intended as a general replacement for a mouse as the primary pointing and navigation device for desktop computers.

Graphics tablet is most suited for artists and those who want the natural feel of a pen like object to manipulate the cursor on their screen. Wacom is the most well-known manufacturer of graphics tablets, and incredibly well respected.

 

• Speaker

Computer speakers, or multimedia speakers, are external speakers, commonly equipped with a low­-power internal amplifier. A plug and socket for the external speakers are used to connect it with computer system. Computer speakers range widely in quality and in price. Laptops computers have inbuilt speakers with them.

 

• Microphone

A microphone is an acoustic-­to-­electric transducer or sensor and is used to convert sound signals into electrical signals. It was originally invented by Emile Berliner in 1877, and allows you to record voices or sounds and place them onto computers, generally as a wave file. To connect microphone, one has to insert the plug of it into the back of the computer system [generally written as mic next to it].

Integrated microphones can be found on laptops and some desktop monitors. These Microphones are usually looking like a small hole in front of the computer which when spoken into will record your voice.

 

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