Nibba group: Input-output Devices

Input-output Devices

Generally, we give data and program to the computer. So what we give to the Computer is known as input. Through which device we give the input is called input device. Generally we get information from the computer, So what we get from the computer is called output. Through which device we get output is called output device.

Input devices

An input device presents data to the processing unit in a machine-readable form. Although the keyboard is a common input device for a small computer, a system may also support various other input devices such as Optical Character Recognition (OCR), Magnetic Ink Character Recognition (MICR), mark sense reader, etc.

Key board
The keyboard is very much like a standard typewriter keyboard with a few additional keys. The basic QWERTY layout of characters is maintained to make it easy for the trained typist to use the system. The additional keys are included to perform certain special functions such as loading a program, edition a text, etc. These are known as function keys that vary in number from system to system.

Optical Character Recognition Often abbreviated as OCR,

optical character recognition involves reading text from paper and translating the images into a form that the computer can manipulate. An OCR system enables you to take a book or a magazine article and feed it directly into an electronic computer file.

An MICR can identify characters printed with a special ink that contain particles of magnetic material. This device particularly finds applications in banking industry. Since the MICR system can recognise only certain character styles, the characters have to be accurately formed.

Optical Mark Recognition (OMR)

Optical mark recognition, also called mark sense reader, is a technology where an OMR device senses the presence or absence of a mark, such as pencil mark.OMR is widely used in tests such as aptitude tests.

Bar Code Reader

These devices are generally available in super markets, bookshops, etc. Bar-code readers are photoelectric scanners that read the bar codes or vertical zebra striped marks, printed on product containers. Supermarkets use a bar code system called the Universal Product Code (UPC). The bar code identifies the product to the supermarket’s computer which has a description and the latest price of the product. The computer automatically tells the Point of Sales (POS) terminal what the price is.

Digitizing Tablet
This is an input device that enables you to enter drawings and sketches into a computer. A digitizing tablet consists of an electronic tablet and a cursor or pen. A cursor (also called a puck) is similar to a mouse, except that it has a window with cross hairs for pinpoint placement, and it can have as many as 16 buttons. A pen (also called a stylus) looks like a simple ballpoint pen but uses an electronic head instead of ink. The tablet contains electronic field that enables it to detect movement of the cursor or pen and translate the movements into digital signals that it sends to the computer. Digitizing tables are also called digitizers, graphics tables, touch tables or simply tables.

Scanner Scanner
is an input device that can read text or illustrations printed on paper and translate the information into a form that the computer can use. A scanner works by digitizing an image - dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen and manipulated by programs. Optical scanners do not distinguish text from illustrations, they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR) system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages.

Mouse
Mouse is a device that controls the movement of the cursor or pointer on a display screen. It is a small object you can roll along a hard and flat surface. As you move the mouse, the pointer on the display screen moves in the same direction.Mouse contains at least one button and sometimes as many as three, which have different functions depending on what program is running.

Light Pen
Light pen is an input device that utilizes a light-sensitive detector to select objects on a display screen.

Speech input devices
Speech or voice input devices convert a person’s speech into digital form. These input devices, when combined with appropriate software, form voice recognition systems. These systems enable users to operate microcomputers using voice commands.

Output Devices
Output devices receive information from the CPU and present it to the user in the desired form. Output devices include display screen, loudspeakers, printers, plotters, etc.

Display Screen
When a program is keyed in, the screen (which is similar to a television screen) displays the characters. The user can read the program line by line and make corrections before it is stored or printed on a printer. It is also possible to bring to the screen a portion of the program stored in the external storage for editing. Screen sizes differ from system to system. The standard size is 24 lines by 80 characters. Most systems have provision for scrolling. This facilitates the user to move the text vertically or horizontally on the screens thus bringing to the screen the hidden text. Thus the user can scan through the entire file either to review or to select a particular portion. The cursor on the screen is controlled by the cursor keys on the keyboard,

Printer

Printer is a device that prints text or illustrations on paper and in many cases on transparencies and other media. There are many different types of printers. In terms of the technology utilized, printer fall into the following categories.
(i) Ink-jet Printer
Ink-jet printers work by spraying ionized ink on a sheet of paper. Magnetized plates in the ink’s path direct the ink onto the paper in the desired shapes. Inkjet printers are capable of producing high quality print approaching to that produced by laser printers. A typical ink-jet printer provides a resolution of 300 dots per inch, although some newer models offer higher resolutions. In general, the price of ink-jet printers is lower than that of laser printers. However, they are also considerably slower. Another drawback of ink-jet printers is that they require a special type of ink that is apt to smudge on inexpensive copier paper. Because ink-jet printers require smaller mechanical parts than laser printers, they are specially popular as portable printers. In addition, colour ink-jet printers provide an inexpensive way to print full-colour documents.

Laser printer
Laser Printer utilizes a laser beam 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. This is also the way copy machines work. Because an entire page is transmitted to a drum before the toner is applied, laser printers are sometimes called page printers. There are two other types of page printers that fall under the category of laser printers even though they do not use lasers at all. One uses an array of LEDs to expose the drum, and the other uses LCDs. Once the drum is charged, however, they both operate like a real laser printer. One of the chief characteristics of laser printers is their resolution - how many dots per inch (dpi) they lay down. The available resolutions range from 300 dpi at the low end to 1,200 dpi at the high end. By comparison, off set printing usually prints at 1,200 or 2,400 dpi. Some laser printers achieve higher resolutions with special techniques known generally as resolution enhancement. In addition to text, laser printers are very adept at printing graphics. However, you need significant amounts of memory in the printer to print high resolution graphics. To print a full-page graphic at 300 dpi, for example, you need at least 1 MB (megabyte) of printer RAM. For a 600-dpi graphic, you need at least 4 MB RAM. The speed of laser printers ranges from about 4 to 20 pages of text per minute (ppm). A typical rate of 6 ppm is equivalent to about 40 characters per second (cps).

(iii) Line Printer
Line printers are high-speed printers capable of printing an entire line at one time. A fast line printer can print as many as 3,000 lines per minute. The disadvantages of line printers are that they can print only one font, they cannot print graphics, the print quality is low, and they are very noisy.

(iv) Thermal printer
Thermal printers are printers that produce images by pushing electrically heated pins against special heat-sensitive paper. Thermal printers are inexpensive and are used in most calculators and many fax machines. They produce low quality print, and the paper tends to curl and fade after a few weeks or months.