Neon-komputadór

Video Hardware

Video hardware consists of two components. The monitor, or Visual Display Unit, that sits on top of the system unit (or alongside in the case of the tower and minitower chassis) and the video card or adapter, that resides in the system unit attached to the motherboard. The adapter acts as an interface between the computer and the monitor and includes its own Video BIOS, a processor, memory and driver, along with a digital to analog converter. Over time, there has been a steady increase in the resolution and colours of monitors. The main four in use today are VGA (Video Graphics Array), SVGA (Super VGS), XGA (Extended Graphics Array), and UVGA (Ultra VGA). Monitors express resolution in the number of horizontal and vertical picture elements, or pixels, on the screen. The higher the number the greater the detail. VGA has a standard resolution of 640x480, SVGA at 800x600, XGA at 1024x768 and UVGA at 1280x1024. Unlike the rest of the electrical world video displays have moved from digital to analog rather than the other way around, as the colour depth achieved is far greater.

Monitors come in a variety of technologies, the most common on the desktop being the cathode ray tube (CRT). This consists of three main components, an electron gun at one end, a vacuum tube in the middle and a phosphorus coated screen at the other end. The electron gun is heated and fires a burst of electrons towards the screen, which are directed by a coil and focus to specific points on the screen. When phosphorus is struck by an electron, it glows. And that's what you see on the screen. The beam moves very quickly, according to a pattern called a 'raster', from the left to right from top to bottom. Because the image fades quickly, the beam must keep a high refresh rate (also known as vertical scan frequency). Most CRT monitors have a refresh rate of 85 hertz (Hz), or 85 times per second.

An alternative monitor technology is LCD displays; most commonly found on laptop computers, but now also found on desktop machines. LCDs are low glare, completely flat screens and consume about 1/20th of the power of a CRT monitor (5 watts vs 100 watts). The colour quality is considered superior. However, they also cost a little more than twice the amount of a similar CRT monitor - but in the long run however they are most cost-efficient. In a LCD, a polarizing filter creates two light waves, blocking out those not aligned with the filter. A second filter, by changing the relative angle to the first, changes the amount of light that can be passed through. In a colour LCD each filter has three cells for each pixel - red, green and blue.

Caring For You and Your Monitor

A CRT monitor that has a low refresh rate will cause the screen to flicker and cause eyestrain. Cheap monitors only have flicker-free refresh rates at 640x480 resolution - it should also be tested (and insisted) on higher resolutions such as 1024x768. Avoid video adapters that use interlaced signals as these commonly have such problems. Make sure that the refresh rates expected by a CRT monitor match those produced by the video card - if they are different, an image will probably fail and the monitor will be damaged. Another cause of eyestrain is a dirty monitor. Periodically clean with an alcohol based cleaning agent on a soft cloth (or even better newspaper) applied in a circular fashion.

Using the power management features of a PC, to put it on a low-power standby mode after 10 minutes and to switch it off after 60 minutes can substantially increase the monitor's power supply. To further increase the lifespan of a monitor, ensure that a monitor has adequate ventilation along the sides, rear and top. If a monitor has a degaussing feature, uses this every week or so to remove stray magnetic features. CRTs have powerful magnets around the picture tube, so keep magnetic media away from them (i.e., don't keep your floppy disks on top of your monitor!).

A properly selected monitor can also have substantial energy savings - you may have noticed some with US Environmental Protection Agency's "Energy Star". These are a PC/Monitor combination that consume less than 60 watts during idle periods. It is also worth choosing a monitor that reduces a users exposure to VLF (very low frequency) or ELF (extremely low frequency) electromagnetic emissions (ie., frequencies below that of radio broadcasting). Recent medical studies have linked these electromagnetic emissions to miscarriages, birth defects and cancer. Significant ELF emissions also come from electric blankets and power lines. One easy way to protect oneself from such emissions is to keep your monitor about 60 centimetres (about an arm's length). Some anti-glare screens also cut down on ELF and VLF emissions as well as reducing eyestrain.