As characters are entered using the keyboard, the corresponding data are stored in the memory of the computer. From the memory the data are translated back into a format the end-user understands, and displayed in an output like the monitor.
Such a collection of input and output devices is called a video display terminal (VDT)or cathode ray tube. A video display terminal linked to a computer is referred to as a work station.
A terminal contains a communication link to a main computer. Large computer systems (from microcomputers to supercomputers) have an array of video display terminals linked to its main computer.
The primary input device on most small computer systems is the keyboard. The basic lay-out of the keyboard resembles that of the typewriter but contains additional keys necessary to perform various computer operations. Most keyboards have eight major body parts. These include the main keyboard, function keys, command keys, cursor keys, numeric keys, text editing keys, special keys, and the LED status indicators.
Most software available today are designed to work with the mouse. The mouse is connected to the computer to give users an easier alternative to the key combinations of the cursor keys available in the keyboard.
The mouse contains buttons that can be pressed, providing users the "point and click" operation necessary to by-pass the key combinations of the keyboard cursor keys.
Any movement of the mouse causes related output movement of the cursor on the monitor or screen. The cursor, a graphic figure that appears on the monitor, often as an arrow or cross-hair, is controlled by the mouse.
A software driver is provided by software developers often as a part of the software package to operate the mouse.
The joystick is basically a pointing device commonly used in games. It provides more realistic control for many games.
A joystick is connected to the computer using cable through a "game port." Small sliders are provided to adjust the joystick for different computers. the joystick continuously sends signals to the computer telling it the current position of the handle. The program uses this information to update its actions.
Keystrokes using keyboards will continue to be the basic mode of data entry in the foreseeable future. However, recent technological innovations have eliminated the need for key-driven data entry in some applications. Today, the trend in data entry is towards the elimination of keystrokes whenever possible.
Image scanners scan images or text to be displayed on the monitor or released by the printer.
Scanners can copy an image from its original document to the memory of the computer, store it in disk, adn use it later as part of an electronically generated document.
Optical mark readers convert images, like pencil marks on paper, into signals that the computer can store and do operations on.
Magnetic stripes are often placed on the back of credit cards or ATM cards. Magnetic stripes "read' and 'check" the authorization code written on the magentic stripe before permitting a person to make a transaction or gain entry to certain rooms or buildings.
Monitors or screen enable users to communicate visually with the computer. They provide users temporary 'soft copies"of output results. Monitors are classified according to three basic attributes:
color, size, and resolution.
Monitors can either be in color or monochrome. The size of the monitor corresponds to the diagonal length of the screen, measured in inches. The resolution of the monitor is the number of horizontal and vertical pixels that a monitor can display. Pixel stands for picture element.
Printers provide users permanent "hard copy" outputs. printers are classified according to themeans by which images are transferred on paper.
There are two basic types of printers: impact printers and non-impact printers.
Impact printers transfer image on paper through mechanical means. The mechanical action of print hammers produce hammers produce enough impact to transfer image from the hammer, to the ribbon, and finally to the paper.
Inexpensive dot-matrix printers are widely used today. Daisy-
wheel printers are known for
higher quality output but are more expensive than dot-matrix computers.
Non-impact printers use ink-jet or laser technology. Ink-jet printers are capable of printing in color. Image is transferred on paper through snozzles which spray electrically charged ink across an electrically charged field. Laser printers utilize xerographic technology and produce high-quality outputs. Just like copying machines, laser printers utilize a light scan, drum, and toner that are used to transfer an image of paper.