The terms “input” and “output” are used both as:
verbs to describe the process of entering /displaying the data. nouns referring to the data itself entered into /displayed by the computer.
Input devices are necessary to convert information or data in to a form which can be understood by the computer. A good input device should provide timely, accurate and useful data to the main memory of the computer for processing.
Keyboard is the standard input device attached to all computers.
The layout of a 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.
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. The computer keyboard is used to enter text information into the computer. The keyboard can also be used to type commands directing the computer to perform certain actions.
Commands are typically chosen from an on-screen menu using a mouse, but there are often keyboard shortcuts for giving these same commands. keyboards usually have a numeric keypad, a bank of editing keys, and a row of function keys along the top. Laptop computers don’t have room for large keyboards.
they include a “fn” key so that other keys can perform double duty. Most keyboards attach to the PC via a PS/2 connector or USB port.
The graphical user interfaces (GUIs) in use today requires some kind of device for positioning the on-screen cursor.
Typical pointing devices are:
Pointing devices are connected to a PC via a serial ports (old), PS/2 mouse port (newer), or USB port (newest).
A mouse is an input device that is used on personal computer. It rolls on a small ball and has two or three buttons on the top. When rolled across a flat surface the screen censors the mouse moves in the direction of mouse movement. In older mice, a ball in the bottom of the mouse rolls on the surface as it moves. internal rollers sense the ball movement and transmit the information to the computer via the cord of the mouse. The newer optical mouse uses a light and a small optical sensor to detect the motion of the mouse by tracking a tiny image of the desk surface. Optical mice avoid the problem of dirty mouse ball, which causes regular mice to roll unsmooth. A cordless or wireless mouse communicates with the computer via radio waves. such mice need internal batteries.
A mouse also includes one or more buttons (and possibly a scroll wheel) to allow users to interact with the GUI. The traditional PC mouse has two buttons, while the traditional Macintosh mouse has one button. On either type of computer you can also use mice with three or more buttons and a small scroll wheel.
Most laptop computers have a touch pad pointing device. Moving the on-screen cursor is done by sliding a finger along the surface of the touch pad. The buttons are located below the pad, but most touch pads allow you to perform “mouse clicks” by tapping on the pad itself. Touch pads have the advantage over mice that they take up much less room to use. They have the advantage over trackballs that there are no moving parts to get dirty and result in jumpy cursor control.
Some sub-notebook computers, which lack room for even a touch pad, incorporate a trackpoint. a small rubber projection embedded between the keys of the keyboard. The trackpoint acts like a little joystick that can be used to control the position of the on-screen cursor.
Trackball is sort of like an upside-down mouse, with the ball located on top. A is fingers is used to roll the trackball, and internal rollers sense the motion which is transmitted to the computer. Trackballs have the advantage over mice in that the body of the trackball remains stationary on a desk, so much room is not needed to use the trackball. Early laptop computers often used trackballs.
Some computers, especially small hand-held PDAs, have touch sensitive display screens. The user can make choices and press button images on the screen. Stylus is often used, which you hold like a pen, to “write” on the surface of a small touch screen.
A graphics tablet consists of an electronic writing area and a special “pen” that works with it. A graphics tablet allows artists to create graphical images with motions and actions similar to using more traditional drawing tools.
Joysticks and other game controllers can also be connected to a computer as pointing devices. They are generally used for playing games, and not for controlling the on-screen cursor in productivity software.
A scanner is a device that images a printed page or graphics by digitizing it, producing an image made of tiny pixels of different brightness and color values which are represented numerically and sent to the computer. Scanners scan graphics and pages of text which are then run through OCR (Optical Character Recognition) software that identifies the individual letter shapes and creates a text file of the page’s contents. The common optical scanner devices are:
Magnetic Ink Character Recognition (MICR),
Optical Mark Reader (OMR) ,
Optical Character Reader (OCR).
Magnetic Ink Character Recognition (MICR)
This is widely used by banks to process large volumes of cheques and drafts. Cheques are put inside the MICR, as they enter the reading unit, the cheques pass through the magnetic field which causes the read head to recognize the character of the cheques.
Optical Mark Reader (OMR)
This technique is used when students have appeared in objective type tests and they had to mark their answer by darkening a square or circular space by pencil. These answer sheets are directly fed to a computer for grading where OMR is used.
Optical Character Recognition (OCR):
This technique unites the direct reading of any printed character. Suppose you have a set of hand written characters on a piece of paper. You put it inside the scanner of the computer. This pattern is compared with a site of patterns stored inside the computer. Whichever pattern is matched is called a character read. Patterns that cannot be identified are rejected.
A microphone is attached to a computer to record sound.
The sound is digitized and stored in the computer to later processing and playback.
MIDI (Musical Instrument Digital Interface) is a system designed to transmit information between electronic musical instruments. A MIDI musical keyboard can be attached to a computer and allow a performer to play music that is captured by the computer system as a sequence of notes with the associated timing.
Visual Display Unit (VDU)
The most popular output device is the VDU.
The VDU is also called monitor.
Monitor is used to display the input data and to receive messages from the computer. It has its own box which is separated from the main computer system and is connected to the computer by a cable. In some systems it is compact with the system unit.
It can be color or monochrome.
Traditional output device of a personal computer has been the CRT (Cathode Ray Tube) monitor. It contains a large cathode ray tube that uses an electron beam of varying strength to “paint” a picture onto the color phosphorescent dots on the inside of the screen. CRT monitors are heavy and use more electrical power than flat panel displays. CRT are preferred by some graphic artists for their accurate color rendition, and preferred by some gamers for faster response to rapidly changing graphics. Monitor screen size is measured diagonally across the screen, in inches. Not all of the screen area may be usable for image display, so the viewable area is also specified.
The resolution of the monitor is the maximum number of pixels it can display horizontally and vertically (such as 800 x 600, or 1024 x 768, or 1600 x 1200). Most monitors can display several resolutions below its maximum setting. Pixels (Picture Elements) are the small dots that make the image displayed on the screen. The spacing of the screen’s tiny phosphor dots is called the dot pitch (dp), typically .28 or .26 (measured in millimeters). A screen with a smaller dot pitch produces sharper images.
Computer must produce a video signal that a monitor can display. This may be handled by circuitry on the motherboard, but is usually handled by a video card in one of the computer’s expansion slots; often the slot is a special one dedicated to video use, such as an AGP slot (Accelerated Graphics Port). Video cards are also called video display adapters, and graphics cards. Many video cards contain separate processors and dedicated video memory for generating complex graphics quickly without burdening the CPU.
Flat Panel Monitor
A flat panel display usually uses an LCD (Liquid Crystal Display) screen to display output from the computer. The LCD consists of several thin layers that polarize the light passing through them. The polarization of one layer, containing long thin molecules called liquid crystals, can be controlled electronically at each pixel, blocking varying amounts of the light to make a pixel lighter or darker. Other types of flat panel technology exist (such as plasma displays) but LCDs are most commonly used in computers, especially laptops. Older LCDs had slow response times and low contrast, but active matrix LCD screens have a transparent thin film transistor (TFT) controlling each pixel, so response, contrast, and viewing angle are much improved. Flat panel displays are much lighter and less bulky than CRT monitors. They consume much less power.
They are more expensive than CRTs, but the price gap is narrowing. The display size of a flat panel is expressed in inches, and the resolution is the number of pixels horizontally and vertically on the display.
Terminal is a very popular interactive output unit.
It is divided into two types:
hard copy terminals.
soft copy terminals.
A hard copy terminal provides a printout on paper.
A soft copy terminals provides visual copy on monitor.
Printer is an important output device 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 printers use the familiar typewriter approach of hammering a typeface against the paper and inked ribbon. Dot-matrix printers are of this type. Dot matrix printers use small electromagnetically activated pins in the print head, and an inked ribbon, to produce images by impact. These printers are slow and noisy, and are not commonly used for personal computers anymore they can print multi-layer forms, which neither ink jet nor laser printers can.
Non-impact printers 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.
Ink Jet Printer
For hardcopy output, you need some kind of printer attached to the computer. The most common type of printer for home systems is the color ink jet printer. These printers form the image on the page by spraying tiny droplets of ink from the print head. The printer needs several colors of ink (cyan, yellow, magenta, and black) to make color images. Some photo-quality ink jet printers have more colors of ink. Ink jet printers are inexpensive, but the cost of consumables (ink cartridges and special paper) makes them costly to operate in the long run for many purposes.
A laser printer produces good quality images by the same technology that photocopiers use. A drum coated with photosensitive material is charged, and then an image is written onto it by a laser (or LEDs) which makes those areas lose the charge. The drum then rolls through toner (tiny plastic particles of pigment) that is attracted to the charged areas of the drum. The toner is then deposited onto the paper, and then fused into the paper with heat.
Most laser printers are monochrome, but more expensive laser printers with multiple color toner cartridges can produce color output. Laser printers are faster than ink jet printers.
Their speed is rated in pages per minute (ppm).
They are more expensive than ink jets, but they are cheaper to run in the long term if you just need good quality black & white pages.
Multi-function printers are available that not only operate as a computer printer, but also include the hardware needed to be a scanner, photocopier, and FAX machine as well.
Computers also produce sound output, ranging from simple beeps alerting the user, to impressive game sound effects, to concert quality music. The circuitry to produce sound may be included on the motherboard, but high quality audio output from a PC usually requires a sound card in one of the expansion slots, connected to a set of good quality external speakers or headphones. Multimedia is a term describing computer output that includes sound, text, graphics, movies, and animation. A sound card is an example of a multimedia output device .