Soft Copy Output Devices Of Computer
Normally, the output is produced on the screen of the computer system
. When ever permanent copy is to be produced, users prefer to preview outputs on screens; this allows users to make necessary correction or to rearrange material.
Monitor is a television like device that converts computer information into graphical images and text. When the electron beam has scanned the entire screen and illuminated each pixel, we see a complete image although the computer image never appears on the screen at one time. The image we see is a one traced on the retains of our eyes by the light beam. However, this image will fade unless it is refreshed. Thus the electron beam must scan the screen very rapidly, a minimum of sixty times per second, so that the intensity of the image we see will remain approximately the same and so that the screen will not appear to flicker. Two kinds of display screens are used for monitors
1. Cathode ray tube (CRT) 2. Flat panel display (FPT).
1. Cathode ray tube (CRT)
On this type of screen, a data image can be produced by moving an electron beam across a phosphor-created screen. By intensifying the strength of the beam, the phosphor-coating glows in certain places, forming the characters. The most common type of CRT is 14 inch display screen having 25 lines and 80 characters each. Large monitor sizes including 15 inch, 17 inch and 21 inch monitors are available. Some specialized monitors used in desktop publishing applications can display upto 8 X 11-inch pages at their normal size.
A monochrome or single color CRT usually displays green, amber, or white characters on a black screen. A color monitor is often preferred for output containing graphics. RGB monitors, produce a much sharper picture, because three electron guns allow finer control over the intensive of the phosphor dots. The quality is represented by certain color and resolution characteristics in a monitor and the circuitry that permits them.
2. Fiat panel display (FPT).
A CRT screen is reliable but it is bulky and consumes a lot of power and that is why it is cumbersome to use it with portable computers. For small computers, flat panel display is used. It does not have a picture tube. Flat panel display can be of two types;
Liquid Crystal Display
The most common type of flat panel display is the liquid crystal display (LCD), which produces images by aligning molecular crystals. When a voltage is applied, the crystals line up in a way that blocks light from passing through them and this absence of light is seen as characters on the screen. LCDs are better than CRTs and do not flicker, thereby avoiding eyestrain and fatigue caused by CRT's during prolonged session at the computer.
Gas Plasma Display
Gas plasma display (GDP) work by trapping the electrically charged gas (plasma) particles between glass plates. The plasma at the pixel emits light as the current is applied. Characters are formed by lighting the appropriate pixels. They are becoming popular, but still more expensive than CRTs and LCDs. GDP are used where the quality of the picture and flat panel are the critical consideration.
Pixel
When the electron beam has scanned the entire screen and illuminated each pixel, we see a complete image although the computer image never appears on the screen at one time. The image we see is a one traced on the retains of our eyes by the light beam. However, this image will fade unless it is refreshed. Thus the electron beam must scan the screen very rapidly, a minimum of sixty times per second, so that the intensity of the image we see will remain approximately the same and so that the screen will not appear to flicker.
Resolution
The screen resolution, or detail, possible with a particular monitors determined by the number of pixels that make up the screen. Monitors are currently available with from 64000 to more than 2 million pixels per screen the greater the resolution of the monitor, the greater the storage demand on the computer, since the image must be stored before it can be displayed. Two techniques are used to store the computer images: bit - mapped and character - addressable,
DISPLAY
Virtually everyone who interacts with a computer system today uses some type of Display device. These peripheral hardware units consist of a television-like viewing screen, to which computer output is sent. The two most common types of display are monitors and terminals.
Monitor (display monitor) a television like device that converts computer information into graphical images and text.
Terminal hardware consisting of a keyboard and display screen allowing a user to communicate with a computer either through normal cable connections or by a network.
by: Rashid Javed
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