All monitors do the same thing: they take a video signal from a computer and display it on a screen. However, there are several different types of connection, and several different types of screen.
With current technologies, it's simplest to use an HDMI cable to connect the HDMI port on a PC to the HDMI port on a flat-screen LCD monitor. HDMI (High-Definition Multimedia Interface) handles both high-def video and up to eight sound channels in a single cable. Either way, it's useful if both the computer and screen use the same port, or if a cheap adaptor can be used to make the connections compatible.
Alternatives to HDMI include single-link Digital Visual Interface (DVI-D) and the royalty-free DisplayPort. Remember to check the video-out ports on your PC before buying a new monitor for it, while avoiding the antique analogue standby, VGA (Video Graphics Array).
The types of monitor
CRT: Traditional computer displays were based on large, glass cathode ray tubes (CRTs) of the sort used for television sets. They are rapidly falling out of use because large displays require bulky and extremely heavy CRTs.
LCDs: Today, most PCs are used with backlit liquid crystal display (LCD) screens, which first became popular on laptop computers. LCDs are also used for mass-market TV sets, up to about 40-in screens. Beyond that, it is hard to make LCDs economically, partly because large areas will tend to include some bad pixels (picture elements).
Plasma: Plasma screens are made using tiny gas-filled cells that work like neon tubes, so it's relatively easy to manufacture screens that are bigger than about 40 inches. However, they are generally too large and too expensive for PC use.
OLED: Some companies, such as Sony and Samsung, are pioneering flat screens made with organic light emitting diode (OLED) materials that don't need backlighting. They offer much better colour contrast than LCDs, from bright highlights to intense blacks, but they still cost too much for most purposes. Small OLED screens are now being used in some digital cameras and mobile phones.
You may also see TFT or LED screens advertised. These are still LCD screens. TFT LCDs use thin-film transistor (TFT) technology to provide better image quality. LED screens are LCDs backlit using light-emitting diodes (LEDs) instead of cold cathode fluorescent lamps. Some LCD screens also use IPS (in-plane switching) to provide wider viewing angles.
There are three more things to consider when buying an LCD screen: the screen size, the aspect ratio, and the resolution.
LCD screens come in a wide range of sizes from about 12 inches to 30 inches, measured across the diagonal. Bigger is better, but costs more. A 30-inch LCD can cost 10 times as much as a small entry-level model. Today, screen sizes from about 21-24 inches are an economical compromise.
Most computer and TV screens used to have an aspect ratio of 4:3, but today, most are widescreens. In computing, a screen ratio of 16:9 is now the most common for new purchases, and some LCD monitors include built-in TV tuners and speakers.
Every LCD screen also has a standard resolution that your computer will need to support. The screen image is made up of millions of dots or pixels, so the more pixels there are, the better the resolution.
A typical 4:3 screen had a resolution of 1024 x 768 pixels, which is known as XGA (eXtended Graphics Array). A superior 5:4 ratio screen had a resolution of 1280 x 1024 pixels (Super XGA or SXGA), which is 1.3 megapixels.
Modern 16:9 widescreens are usually described as HD, HD Plus (HD+), or Full HD. An HD (high definition) screen will have a resolution of 1366 x 768 pixels, which is very common on laptops. An HD+ screen will have a resolution of 1600 x 900 pixels, while a Full HD screen will do 1920 x 1080 pixels. This reflects the changing definition of high-def movies and TV channels, which started with 720p (that is, moving images with a resolution of 1280 x 720 pixels). "Full HD" is now used for 1080p movies (1920 x 1080 pixels) and the corresponding screens.
The screen resolution is somewhat independent of screen size. A 17-inch HD+ screen will show exactly the same information as a 22-inch HD+ screen: 1600 x 900 pixels. As a result, everything on the 22-inch screen - programs, icons, text, etc - will be physically larger.
In general, allowing 100 pixels per inch provides a comfortable screen for computer work. A Full HD screen should therefore measure about 19.2 x 10.8 inches, which is what you get with a 22-inch widescreen LCD. A bigger screen may be better if you have impaired vision, or plan to watch videos, or want to place the screen further away. Alternatively, you can sit slightly closer to a smaller screen.