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Video Cards And
Monitors
The video controller
card is the interface between the monitor and the computer. These cards
are sometimes called graphic adapters, video boards, graphics cards, or
display cards. Sometimes the video controller is integrated into the
systemboard. If you are buying a systemboard with this integrated video
controller, check that you can disable the controller on the systemboard
if it needs replacement or gives you trouble. You can then install a video
card and bypass the controller on the systemboard. The quality of a video
subsystem is rated according to how it affects overall system performance,
video quality (including resolution and color), power-saving features, and
ease of use and installation. The video controller is separate from the
core system functions, so manufacturers can use a variety of techniques to
improve performance without worrying about compatibility with systemboard
functions. An example of this flexibility is seen in the many different
ways memory is managed on a video controller.
Video Cards
A video card is an
expansion card responsible for the following:
Receiving data and
instructions from the CPU Processing the data Sending the data to the
monitor. If your video card is not on the list of provided drivers, you
might be able to locate it on the Internet. Four basic functions occur on
the video card, as seen in the following figure:
Four Basic Functions
of a Video Card
(1) The digital data
arrives from the system bus to the video chip set on the video card.
(2) The video chip
set writes the digital data to video memory on the card.
(3) The data stored
in video memory is passed to the digital analog
converter
(RAM DAC).
(4) RAM DAC passes
the analog data to the monitor.
RAM DAC Technology
The RAM DAC technology
may be housed on a single RAM DAC chip on the video card or it may be
embedded in the video chip set. RAM DAC includes three digital-to-analog
converters, one for each of the monitor’s three color guns: red, green,
and blue (RGB).
Video Card Buses
The speed and
performance of a video card are partly a function of the bus that the card
is using. Since 1995, video cards have been designed to use only the PCI
bus and more recently to use the AGP slot. Older video cards were made to
run on VESA local buses (VL-bus), a proprietary local bus, ISA buses, and
EISA buses. The fastest bus for video on a systemboard today is AGP with a
32-bit-wide data bus, running at up to 1 GB/sec, depending on the AGP
standard used. The regular AGP slot has 132 pins and AGP Pro has 188 pins.
The added pins used by the AGP Pro standard provide voltage for high-end
graphic accelerator cards discussed in the next section. After AGP, the
PCI bus is next in throughput, providing either 132 or 264 MB/sec. If you
play computer games or use extensive graphics software, such as that for
CAD or desktop publishing, invest in a fast video card that uses a fast
bus and has plenty of memory.
On the video card
itself, performance is affected by the chip set, memory, and the RAM DAC,
as well as by the bus speed and size. One method to improve performance is
to allow both the video chip set and the RAM DAC (both the input and the
output processes) to access video memory at the same time. This method,
called dual-porting, requires a
special kind of video RAM. Another method of increasing performance is to
place a processor on the video card, making the card a
graphics accelerator.
The bus external to the
video card is the PCI bus or the AGP bus, but the card itself also has an
internal video bus. The volume of data that can travel on the bus is
called bandwidth.
Current video buses use
a data path that may be 32 bits, 64 bits, 128 bits, or even 256 bits wide.
The effective bandwidth of the bus is partly determined by the width of
the data path and the amount of memory on the card.
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