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Figure 19-29 A traditional CRT connector

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NOTE You’ll often hear the terms flat-panel display or LCD panel to describe LCD monitors. I prefer the term LCD monitor, but you should be prepared to hear it a few different ways.

Unlike the analog CRTs, LCD monitors need a digital signal. This creates somewhat of an issue. The video information stored on a video card’s RAM is clearly digital. All VGA and better video cards include a special chip (or function embedded into a chip that does several other jobs) called the random access memory digital-to-analog converter (RAMDAC). As the name implies, RAMDAC takes the digital signal from the video card and turns it into an analog signal for the analog CRT (see Figure 19-30). The RAMDAC really defines the bandwidth that the video card outputs and can lso convert digital to analog.

Well, RAMDACs certainly make sense for analog CRT monitors. However, if you want to plug your LCD monitor into a regular video card, you need RAMDAC on the LCD monitor to convert the signal from analog to digital (see Figure 19-31).

Many LCD monitors use exactly this process. These are called analog LCD monitors. The monitor really isn’t analog; it’s digital, but it takes a standard VGA input. These monitors have one advantage: You may use any standard VGA video card. But these monitors require adjustment of the analog timing signal to the digital clock inside the monitor.

Figure 19-30 An analog signal sent to a CRT monitor

This used to be a fairly painful process, but most analog LCD monitors now include intelligent circuitry to make this process either automatic or very easy.

Why convert the signal from digital to analog and then back to digital? Well, many monitor and video card people agree that it just doesn’t make much sense. We now see quite a few digital LCD monitors and digital video cards. They use a completely different connector than the old 15-pin DB connector used on analog video cards and monitors. After a few false starts with connection standards, under names such as P&D and DFP, the digital LCD world, with a few holdouts, moved to the digital visual interface (DVI) standard. DVI is actually three different connectors that look very much alike: DVI-D is for digital, DVI-A is for analog (for backward compatibility if the monitor maker so desires), and the DVI-A/D or DVI-I (interchangeable) accepts either a DVI-D or DVI-A. DVI-D and DVI-A are keyed so that they will not connect.

DVI-D and DVI-I connectors come in two varieties, single-link and dual-link. Single-link DVI has a maximum bandwidth of 165 MHz, which, translated into practical terms, limits the maximum resolution of a monitor to 1920 × 1080 at 60 Hz or 1280 × 1024 at 85 Hz. Dual-link DVI uses more pins to double throughput and thus grant higher resolutions (Figure 19-32). With dual link, you can have displays up to a whopping 2048 × 1536 at 60 Hz!

Figure 19-31 Converting analog back to digital on the LCD

Figure 19-32 Dual-link DVI-I connector

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NOTE You can plug a single-link DVI monitor into a dual-link DVI connector and it’ll work just fine.

Digital connectors are quickly replacing analog in the monitor world. Digital makes both the monitor and the video card cheaper, provides a clearer signal because no conversion is necessary, and makes installation easy. Many monitors and video cards these days only support digital signals, but there are still quite a few of each that provide both digital and analog connections.

The video card people have it easy. They either include both a VGA and a DVI-D connector or they use a DVI-I connector. The advantage to DVI-I is that you can add a cheap DVI-I to VGA adapter (one usually comes with the video card) like the one shown in Figure 19-33 and connect an analog monitor just fine.

Figure 19-33 DVI to VGA adapter

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NOTE Video cards with two video connectors support dual monitors. See the “Dual Monitors” section later in this chapter.