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Lesson 3 X-related hardware considerations
Objective Factors that influence the installation of XFree86

XFree86-related Hardware Considerations

What are the factors that influence the installation of XFree86?
Before you install XFree86, you must be aware of your system's video hardware. The video hardware affects how many colors can be displayed, how many pixels the desktop can hold, and how comfortable the X viewing will be. The installation procedure prompts you for several hardware parameters, including:
  1. Video card chipset
  2. Amount of video memory
  4. Monitor scan rates

Several X servers exist, each built to take advantage of particular hardware capabilities. Your video card's chipset[1] determines which server is installed.

Amount of Memory

The video card's chipset is a processor built for the express purpose of displaying information on a monitor. The amount of memory determines the highest displayable resolutions and color depths. For instance, in the installation simulation you saw a reference to a video mode with 32-bit color depth on a screen of 1280x1024 pixels.
High-resolution modes (those above 1280x1024) produce sharper images, but can decrease system performance.


No, RAMDAC video cards are not still being used today in modern computers to convert the digital signal. RAMDAC stands for Random Access Memory Digital-to-Analog Converter. It is a chip that is used in graphic cards to convert digital signals from the computer's memory into analog signals that can be displayed on a monitor. RAMDACs became obsolete as DVI, HDMI, DisplayPort and other digital interface technology became mainstream, which transfer video data digitally (via transition-minimized differential signaling or low-voltage differential signaling) and defer digital-to-analog conversion until the monitor's pixels are actuated.
Modern video cards have integrated RAMDACs, which are built into the GPU chip. These integrated RAMDACs are more efficient and can support higher resolutions and refresh rates than discrete RAMDACs. If you are using a modern computer with a digital monitor, you do not need to worry about RAMDACs. The GPU will handle the conversion of the digital signal to an analog signal for you. A video card's RAMDAC converts the digital signal created by the chipset to the analog signal required by the monitor. You will not need this information for configuration, unless you use xf86config with some older cards.

Scan Rates

A monitor's scan rates[2] determine how often pixels are redrawn. The video card must produce data at a rate compatible with the monitor's scan rates. Consequently, the X server needs to know this information so it can instruct the video card appropriately.

Monitor's Capabilities

Knowledge of the monitor's capabilities is absolutely critical. Specifying incorrect scan rates when configuring X can permanently damage the monitor. Consult the monitor's user manual or ask the manufacturer if there is any doubt about its capabilities.
The next lesson explains the various methods to obtain video card specifications.

XWindows Fundamentals Quiz

Before moving on to the next lesson, click the Quiz link below to check your understanding of what an X server does and how available hardware affects the configuration.
XWindows Fundamentals - Quiz

x = - b ± b 2 - 4 a c 2 a
[1]Chipset: The particular graphics processing system used on a particular video card.
[2]Scan rates: The rate at which horizontal scan lines are drawn on the monitor and the rate at which one entire sweep of the screen is made. These are referred to as the horizontal and vertical scan rates.