Hardware Reference
In-Depth Information
The benefits of increasing the RAMDAC speed include higher vertical refresh rates,
which allow higher resolutions with flicker-free refresh rates (72Hz-85Hz or above) on
CRT displays. Typically, cards with RAMDAC speeds of 300MHz or above display
flicker-free (75Hz or above) at all resolutions up to 1920×1200 on CRT displays. Of
course, as discussed earlier in this chapter, you must ensure that any resolution you want
to use is supported by both your monitor and video card.
Video Display Interfaces
Video display adapters connect a PC to a display and therefore must work through two
main interfaces. The first is the system interface, meaning the connection between the
video adapter and the PC, and the second is the display interface, meaning the connection
between the video adapter and the display. By using standardized versions of these inter-
faces, we end up having video adapters and displays that are both compatible and easily
interchangeable.Thissectiondiscussestheavailablesystemanddisplayinterfacesaswell
as the differences between them.
The System Interface
Older video adapters were designed for use with earlier bus standards, such as the IBM
MicroChannel Architecture (MCA), Interactive Multimedia Association (ISA), Enhanced
Interactive Multimedia Association (EISA), and VESA local bus (VL-Bus). Because of
theirrelativelyslowperformancebytoday'sstandards,allarenowobsolete.Currentvideo
display adapters use PCIe interface standards to connect to a system, although older sys-
tems based on Accelerated Graphics Port (AGP) are still relatively common. Peripher-
al Component Interconnect (PCI)-based adapters are still found in some old systems or
AGP-based systems that utilize a second adapter.
See
“
The PCI Bus
,”
p.
232
(
Chapter 4
).
See
“
PCI Express
,
”
p.
235
(
Chapter 4
)
.
See
“
Accelerated Graphics Port
,
”
p.
237
(
Chapter 4
)
.
AGP
The AGP, an Intel-designed dedicated video bus introduced in 1997, delivers a maximum
bandwidth up to 16 times greater than that of a comparable PCI bus. AGP was the main-
streamhigh-speedvideo-to-systeminterfaceforseveralyearsbuthasbeenreplacedbythe
more versatile and faster PCIe standard.
TheAGPslotisessentiallyanenhancementtotheexistingPCIbus;however,it'sintended
for use only with video adapters and provides them with high-speed access to the main
systemmemoryarray.Thisenablestheadaptertoprocesscertain3Dvideoelements,such
