Input Output Devices

A computer system can be proved to be useful only when it is able to communicate with its external environment. The input-output (1/0) devices provide the means of communication between the computer and the outer world. They are also known as peripheral devices because they surround the CPU. Input devices are used to enter the data in the primary storage and output devices are used to accept the result from the primary storage and store them on the secondary storage area for further processing.
A wide variety of I/O devices are now available.

INPUT DEVICES

Keyboards

Keyboard, the most common input device operated with fingers provide various tactile responses. Various kinds of keys are present on keyboard which perform various functions. Mouse
A mouse is the standard pointing tool for interacting with a graphical user interface. You can select and open files and folders with this pointing device. All Macintosh computers require a mouse whereas on PCs mouse are recommended for additional help. A keyboard can do all the function which mouse can perform.

Trackballs

Trackballs are similar to mouse, except that the cursor is moved by using one or more fingers to roll across the top of the ball.

Touchscreen

Touchscreen are monitors that usually have a textured coating across the glass face. This coating is sensitive to pressure and registers the location of the user's finger when it touches the screen. They are excellent for multimedia applications in a kiosk, at a trade show or in a museum delivery system.

Magnetic card encoder and reader

Magnetic card setups are useful when you need an interface for a database application or multimedia project that tracks users. You need both a card encoder and a card reader for this type of interface. The encoder connects to the computer at a serial port and transfers information to a magnetic strip of tape on the back of the card. The card reader then rends the information encoded on the card.

Graphic tablets

Flat surface input devices are attached to the computer in the same way as a mouse or trackball. A special pen is used against the pressure sensitive surface of the tablet to move the cursor. Graphic tablets provide substantial control for editing finely detailed graphic element, a feature very useful to graphic artists and interface designers. They are used in 3D drawings.

Scanners

A scanner is an input device which scan images, photographs, text, pictures and images of items like stones, cloth etc. The images are stored in digital format at a resolution which can vary.

Digital cameras

Digital cameras such as apple quicktake, the dycam 10c, kodak Dc40 etc. can record up to 50 images on a reusable two inch floppy disk. Images can be played back directly from the camera to any standard TV monitor or used with a digitizer for computing input.
Software controls the image capture, image adjustment and save functions of the digitizer. Once the image is saved in the computer environment, it can be exported to various applications, incorporated into desktop publishing setups, used to enhance a database, or added as a graphic image to a multimedia presentation.

OUTPUT HARDWARE

Amplifiers and speakers

Speakers with built in amplifiers or attached to an external amplifier are important when your project will be presented to a large audience or in a noisy setting.

Monitor

A wide variety of monitors are available for Macintoshes and PCs. Serious multimedia developers will often attach more than one monitor to their computers, using add-on graphics board.

Printer

Till now we have seen everything on the screen. This copy of the document visible on the screen is called the soft copy. But, it is incomplete until we take a print of the document on the paper.
Hard copy of the document is the impression of the document on paper. Printer is a media or an output device, which performs this operation.
A most convenient and useful method by which the computer can deliver information is by mean of printed characters.
A printer falls into two broad categories.

• Impact Printers
• Non Impact Printers

IMPACT PRINTERS

In the impact printers, there is mechanical contact between the print head and paper.
The impact printers can further be classified into following categories:

• Line Printers
• Character Printers

Line printers

A line prints a complete line at a time printing speed vary from 150 lines to 2500 lines per minute with 90 to 100 characters on 15 inch line.
There are 2 types of line printers

• Drum Printer
• Chain Printer

Drum Printer

A drum printer consists of a cylindrical drum on which characters are embossed.
One complete set of characters is embossed for each and every print position on a line. Thus a printer that can print up to 132 characters per line and has a 96 character set will have on its surface 132 x 96 = 12672 characters embossed.
Working of a drum printer
1. The codes of all characters to be printed on one line are transmitted to a storage unit reserved for printer known as printer buffer.
2. The printer drum is rotated at a high speed.
3. A set offprint hammers one for each character in a line is mounted in front of a drum.
4. The position of each character on a bend of the drum surface is coded using its angular displacement from the origin.
5. Striking a hammer against the embossed character in the surface prints a character.
6. A carbon ribbon and paper are interposed between the hammer and the drum as the drum rotates the hammer waits and is activated when the character to be printed at the position appears in front of the hammer.
Thus the drum would have to complete one full revolution for a line to be printed.
This is called "on the fly". Printing as a drum continues to rotate at a high speed when the hammer strikes it.
Disadvantages of drum printer

• The hammer must strike very quickly and must be accurately synchronized with drum movement, if the hammer striking is missed time then the printed line looks wavy and slightly blurred.
• Printer drums are expensive and cannot be changed often.
• Drum printers have a fixed font.

Chain Printer

A chain printer consists of a steel band on which the characters are embossed.
Working of a chain printer

• To print a line, the characters in the line are transmitted in the memory to printer buffer.
• The band is rotated at a high speed.
• With the rotation of a band, a hammer is activated when the desired character as specified in the buffer register comes in front of it.
• Thus a printer with 132 characters per line, 132 hammers will be positioned to strike the carbon ribbon which is placed between the chain, paper and the hammer.
• There should be accurate synchronization between the hammer movement and chain movement as the bad synchronization leads to blurred lines.

Line printers are normally designed for heavy printing applications and can print continuously for a few hours.

Character printer

(Serial printer)

Character printer prints one character at a time, with the print had moving across a line, serial printer normally print 30 to 300 characters per second.
Broadly serial printers may be divided into 2 categories

• Dot Matrix Printer
• Letter Quality Printer

Dot matrix printer

It is the most popular serial printer.
In DMP's the printing head contains the vertical array of pins. Head moves across the paper, selected pins fire against and inked ribbon form a pattern of dots on the paper,

Features of a dot matrix printer

• In the DMP's the capital letter are formed by 5 x 7 matrix of dots i.e., 5 dot rows and 7 dot columns.
  Though there are 9 pins in the print head. The bottom 2 ping are used to form the descenders of small letters link f, g, q, w, e, r, t, y etc.
• Characters to be printed are sent 1 character at a time from the memory to the printer.
• The character code is decoded by the printer electronics that activates the appropriate pins in the print head.
• Many DMP's are bi-directional i.e. they can print the characters from either direction left or right. This speeds up the printing process.
• DMP's are very versatile since with the pin sets, characters of any language other than English can be printed, even the graphics can be printed with DMP's.
• DMP's with 24 pins in the print head are also available in the market.
• These DMP's have a better print quality. There are 80-column DMP's and 132-column dmp available in the market.
  

Letter quality printing

Daisy wheel printer

The letter quality printers print full characters. The most popular printer of such a type is daisy wheel printer.
Working of a daisy wheel printer

• A daisy wheel printer's print head resembles a daisy flower with its print arms appearing like the petals of the flower while the printing the character is sent to the printer buffer.
• The hub is continuously rotating at high speed and a hammer strikes the appropriate character when it is in the position.

The daisy wheel print can have speed up to 90 cps.

Non Impact Printers

The natural limitations of speed in electromechanical devices and cost considerations have led to the development of printers called non impact printers. These can primarily be categorized as follows.

Electromagnetic printers

By using magnetic recording technique, a magnetic image of what is to be printed can be written on a drum surface. Then this is pressed - onto the paper. Speeds of up to 250 characters per second are obtained in such systems.

Thermal printers

An electric pulse can be converted to heat on selected sections of a printing head or on wires or nibs. When this heat is applied to heat sensitive paper, a character is printed.

Electrostatic printers

For electrostatic printers the paper is coated with a non-conducting dielectric material, which holds charges when voltages are applied with writing "nibs”(heads). These heads write dots on the paper as it passes, as shown in the figure. Then the paper passes through a toner, which contains material with colored particles carrying an opposite charge to that written by the nibs; as a result, particles adhere to the magnetized areas, forming printed characters.

Inkjet printers

Some printers direct a high-velocity stream of ink towards the paper. This stream is deflected, generally by passing it through an electrostatic field such as that used to deflect beams in oscilloscopes. In some systems the ink stream is broken into droplets by an ultrasonic transducer.

Laser printers

These printers make use of office copier technologies. The de output image is written on a copier drum with the help of a light be controlled by a computer. With this certain parts of the drum surf get electrically charged, then this drum surface is exposed to the la beam. These laser exposed area attract a toner that form the image attaching itself (toner ink) to the laser generated charges on the drum the toner is then permanently fused on paper with hot or pressure.

Storage devices

Hard disk

A hard disk is a thin, circular metal plate/ platter coated on both the sides with a magnetic material. A hard disk jack consists of a number of disks. Thus a pack of 10 disks will have 18 surfaces to read and write. All these disks together comprise a hard disk, which has a very high capacity ranging from 2 GB to 40 GB (Giga byte). Each disk is divided into concentric circular tracks to store information.
Information is stored on the disk in the form of tiny invisible magnetic spots. The presence of a magnetized spot represents a 1 bit and the absence represents a 0 bit. A standard binary code called EBCDIC is used for recording data.
Hard disk is fixed permanently inside the system unit and hence it's non-portable. Though it can be taken out of the system unit by detaching it.

Floppy disk

The Floppy disk is also referred to as diskettes or floppies. IBM introduced them in 1972. A floppy is made up of flexible plastic material, which is coated with magnetic oxide. The flexible disk is enclosed within a square plastic or cardboard jacket, often referred to as a cartridge. The jacket gives handling protection to the disk surface. The disk is mounted on the disk drive along with the jacket cover and information is loaded and read through an aperture in the jacket.
Floppy disks are typically 3.5, 5.25 and 8 inches in size. But now a day’s floppies are not in used.
The capacity of a floppy is 1.44 MB. Floppy disks are cheap.