Building your PC:
Monitor and Display

Introduction

The word Monitor is actually derived from Latin where it originally stood for warner or suggester though in English usage the word has come to mean something like 'to observe'. The term is also used in several instances for various elements computer technology, though the colloquial usage is for a 'video display unit'. In this context, a computer display (also known as a monitor or screen) is a term for a computer peripheral that is was originally capable of displaying text (and subsequently still or moving graphics) generated by a computer. Invariably the video data is generated by a graphics card though this may be an integral component of the motherboard.

Monitors:

History:

Early VDUs (video display units) arrived during the 1970s and these were based around simple Cathode Ray Tube (CRT) designs and without any graphics capabilities (only being able to display alphanumeric characters which were often either orange or green on a black background) gained the nickname 'glass teletype' as they effectively mimicked the properties of the previous generation of teletype machine.

In many ways the evolution of computer games, the evolution of graphics cards and monitors were all intimately tied together; one technology driving the other. A better graphics card allowed more colours to be displayed at a higher frame rate which allowed more visually appealing games to be produced. This increased the demand for monitors with higher resolutions and faster scan or refresh rates.

IBM introduced the first colour standard (GCA: Color Graphics Adapter) in 1981. This was a stunning four colours with a resolution of 320 pixels by 200 pixels. In 1984 the EGA standard doubled the number of colours and increased the resolution to 640×350 pixels making it far easier to read text from the screen. In 1987 came the VGA (Video Graphics Adapter) standard from IBM which forms the basis for all subsequent graphics cards and monitors. The VGA standard was extended in 1990 as the Extended Graphics Array (XGA) display was made available by IBM. This offered a 800×600 pixel resolution in true (16.8 million colours) colour and an impressive 1024×768 pixel resolution in 65536 colours.

The standard was extended once more to the Ultra Extended Graphics Array (UXGA). Almost all monitors sold today support this format which can support a palette of colours up to 16.8 million and a resolution up to 1600×1200 pixels. Apart from the overall resolution (the total number of pixels that can be displayed on the screen) and the colour depth another important aspect of a monitor its its refresh rate. This is the number of times a second that all the pixels on a monitor (from the bottom to the top) are redrawn. This controls the 'flicker' of the screen and is a number expressed in Hertz. The human eye flickers on average at 40Hz and a a refresh rate of about this frequency would make a screen flicker noticeably. 50Hz is better (this is the flicker rate of a domestic power supply) but even at this refresh rate flicker can be noticeable. As a result most modern monitors have a refresh rate of somewhere around 72Hz.

Monitors had obviously come a long way from the first very poor resolution models. Resolution and size had increased and though the standard monitor size remained at 14" or 15" prices were falling enough to make 17", 19" and 21" models affordable. Television technology was also influencing CRT design and the late 1990s saw the first flat screens that were truly flat rather than the curved fish-bowl of previous generations. However, large flatscreens were bulky, required lots of room, and were extremely power hungry. This represented almost the final evolution of the CRT-based monitor and though they are cheap these days they are rapidly being replaced by flat-screen monitors.

Liquid Crystal Displays

Although the theory of liquid crystals was presented in 1904 by Otto Lehmann it was not until 1969 that James Ferguson discovered the 'nematic field effect' which allowed liquid crystal elements to be turned on or off by an electric field. The company he formed produce the first functioning LCD display in 1971. By the early 1990s monochrome versions of these displays were being used in the earliest laptops because of their low power consumption. The very first versions were extremely poor as they only worked reflectively and ambient light had to be high for anything to be seen. It took the development of the 'transflective' LCD to make the technology truly useful. These have a low-powered backlight that makes the screen visible even when ambient light levels are low. The need for laptops with colour screens led to the first colour LCDs where each individual pixel is divided into three cells (red, green and blue by the use of filters).

The first LCD screens used passive matrix technology where each individual column or row of the display into a single electrical circuit. Unfortunately this technology is cumbersome and requires a large amount of cabling, making it unsuitable for larger screens or screens with higher resolution. This bottleneck was eventually solved by active matrix technology where each Each pixel has its own dedicated transistor, which allows each column line to access one pixel. When a row line is activated, all of the column lines are connected to a row of pixels and the correct voltage is driven onto all of the column lines. The row line is then deactivated and the next row line is activated. All of the row lines are activated in sequence during a refresh operation. Active-matrix displays are much brighter and sharper than passive-matrix displays of the same size, and generally have quicker response times.

Active Matrix technologies allowed for the development of very large LCD screens so that external displays and even televisions based on the technology could be produced. These soon gained considerable market share and now LCD-based displays predominate in the monitor market. The main reasons being the thinness and lightness of the displays as well as the reduced power consumption compared with equivalent CRTs. However, there are some drawbacks to LCD technology. One of the main ones is that video resolution cannot be manipulated as easily as for CRTs and an LCD display always works best at its 'native resolution'. LCDs also generally have lower contrast that CRTs and this could be a factor if you're intending to work in the image manipulation field. There is also light leakage from the individual pixels so that it's difficult to get a true black on an LCD screen.

The issues above notwithstanding then, in general, an medium sized LCD screen (17" or 19") is probably your best bet as a monitor. Unless you're on a tight budget then you can by a reconditioned second-user CRT monitor very cheaply. It should also be noted that if you're building your PC primarily for gaming and multimedia then you're probably want to think about a widescreen monitor and you may well want to consider a plasma monitor (which has far better contrast ratios) rather than an LCD monitor; though they are also far more expensive.

Monitor Connections

Over the years monitor connections have also changed and though the VGA connector (far left) remains the standard the DVI connector (right) is becoming far more common. There are also two types if DVI connectors DVI-I (analogue) and DVI-D. DVI analogue is compatible with VGA by means of a converter cable but DVI-D is not. Please ensure that your monitor is compatible with your graphics card (for more information on these standards see the page on Graphics Cards.

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