Computer Peripherals

Computer Peripherals:

A computer peripheral is any external device that provides input and output for the computer. 

For example, a keyboard and mouse are input peripherals, while a monitor and printer are output peripherals. Computer peripherals, or peripheral devices, are sometimes called "I/O devices" because they provide input and output for the computer. Some peripherals, such as external hard drives, provide both input and output for the computer.

                                                      1.Card Reader

                                                      2. Printers

                                                      3.Keyboard and Visual Display Units

                                                      4.Magnetic Disk

                                                      5. Magnetic Tape Drive

  

1.Card Reader

                         

            It is one of the most popular Input device, also Low cost and most convenient. Data captured in the form of rectangular holes punched on a crd can be fed into the computer through card reader. This medium in this case 19.3 centi meter in length, 9.5 width and 0.018 cm thickness. The card is divided into 80 columns  marked by the numbers 1 to 80 from left to right. The card is again divided into 12 rows numbered12, 11, 0,1,2,3,4,5,6,7,8,9 from top to bottom. Only one character  can be punched on one column. The digits are represented  by punching hust one hole in the corresponding row position. Alphabets are occupy two holes, The codes are  as  follows. A to I is 12,  respective row positions are 1 to 9,  For J to R combination is 11,  S to Z combination is 0. In the case of special characters a combination of two or three holes is used.

            Data can be captured  on card by punching through  a card punching Machine.The card reader only reads the card one after another, It reads sequential manner. The speed of card reader can vary depending on the model. Usually, the speed range between 300 to 1200 cards per minute.

2. Printers

Printer   is an important output device which can be used to get a printed copy of the processed text or result on paper. There are different types of printers that are designed for different types of applications. Depending on their speed and approach of printing, printers are classified as impact and non-impact printers. Impact printers use the familiar typewriter approach of hammering a typeface against the paper and inked ribbon. Dot-matrix printers are of this type. Non-impact printers do not hit or impact a ribbon to print. They use electro-static chemicals and ink-jet technologies. Laser printers and Ink-jet printers are of this type. This type of printers can produce color printing and elaborate graphics.

Serial Printer:

                                              

            The head moves along the line as the characters are printed. Depending up on the width of the stationery (25 to 35 cm), a serial printer can print a maximum of 74 to 132 characters in a line. The print head of a serial printer is bidirectional. (Moving left to right as well as right to left).Control operations can be performed by sending special character code to the printer.

Dot Matrix Printer:

                                            

A type of printer that produces characters  by striking pins against an ink ribbon to print closely spaced dots . Print head of a dot matrix printer consists of a column of 7 or 9 small needles. A character printed by a dot matrix  printer appears as a matrix pattern of dots.A character can formed to a matrix of 7 X 5 dots is also popular,(9 X 7 dots).Dot-matrix printers are relatively expensive and do not produce high-quality output. They can print to multi-page forms (that is, carbon copies), something laser and ink-jet printers cannot do.

Dot-matrix printers vary in two important characteristics:

·         speed: Given in characters per second (cps), the speed can vary from about  80 to 220 cps. Most dot-matrix printers offer different speeds depending on the quality of print desired.

·         print quality: The quality of this type of printing is poor because the character appear as patterns of dots.

Letter Quality Printer:

                                                   

                The matrix patterns are usually 18 X 36 or more. Most letter quality printer operate in one of the two modes. Draft mode(9 X 7) and letter quality mode (18 X 36). In letter quality mode, the speed is usually 50 to 100 cps. Higher speed is achieved when the printer is used in draft mode.

Daisy Wheel Printer:

                             

 

A daisy-wheel printer works on the same principle as a ball-head typewriter. The daisy wheel is a disk made of plastic or metal on which characters and numeric [96] characters stand out in the outer edge. To print a character, the printer rotates the disk until the desired letter is facing the paper. Then a hammer strikes the disk, forcing the character to hit an ink ribbon, leaving an impression of the character on the paper. Daisy-wheel printers cannot print graphics, and in general they are noisy and slow. Speed: printing from 25 to 60 characters per second.

3. Keyboard and Visual Display Units:

 This is the standard input device attached to all computers. The layout of keyboard is just like the traditional typewriter of the type QWERTY. It also contains some extra command keys and function keys. It contains a total of 101 to 104 keys. A typical keyboard used in a computer is shown in the above Fig. You have to press correct combination of keys to input data. The computer can recognize the electrical signals corresponding to the correct key combination and processing is done accordingly.

A device incorporating a cathode ray tube (CRT) display, a keyboard and a serial port. A VDU usually also includes its own display electronics which store the received data and convert it into electrical waveforms to drive the CRT. VDUs fall into two categories: dumb terminals and intelligent terminals (sometimes called "programmable terminals").  Early VDUs could only display characters in a single preset font, and these were confined to being layed out in a rectangular grid, reproducing the functionality of the paper-based teletypes they were designed to replace.  Later models added graphics facilities but were still driven via serial communications, typically with several VDUs attached to a single multi-user computer. This contrasts with the much faster single bitmap displays integrated into most modern single-user personal computers and workstations.  The term "Display Screen Equipment" (DSE) is used almost exclusively in connection with the health and safety issues concerning VDUs.

4.Magnetic Disk:

                                                 

Magnetic disks are most popular for direct access storage device. Each disk consists of a number of invisible concentric circles called tracks. Information is recorded on tracks of a disk surface in the form of tiny magnetic spots. The presence of a magnetic spot represents one bit and its absence represents zero bit. The information stored in a disk can be read many times without affecting the stored data. So the reading operation is non-destructive. But if you want to write a new data, then the existing data is erased from the disk and new data is recorded.

                          

5. Magnetic Tapes:

                                            

Magnetic tapes are used for large computers like mainframe computers where large volume of data is stored for a longer time. In PC also you can use tapes in the form of cassettes. The cost of storing data in tapes is inexpensive. Tapes consist of magnetic materials that store data permanently. It can be 12.5 mm to 25 mm wide plastic film-type and 500 meter to 1200 meter long which is coated with magnetic material. The deck is connected to the central processor and information is fed into or read from the tape through the processor. It similar to cassette tape recorder.

Advantages of Magnetic Tape:

• Compact: A 10-inch diameter reel of tape is 2400 feet long and is able to hold 800, 1600 or 6250 characters in each inch of its length. The maximum capacity of such tape is 180 million characters. Thus data are stored much more compactly on tape.
• Economical: The cost of storing characters is very less as compared to other storage devices.
• Fast: Copying of data is easier and fast.
• Long term Storage and Re-usability: Magnetic tapes can be used for long term storage and a tape can be used repeatedly without loss of data.