Nick said:
I have an older computer with an Intel D845EBG2
motherboard...currently running a 64mb video card...can this mb handle
a 256 or 512mb video card?
The memory on the video card is independent of the motherboard.
/ Video_Memory (512MB)
/ |
Video_Card GPU
\ |
\ AGP_Slot
|
AGP_Bus
|
Northbridge -- DDR266_System_RAM
|
CPU on motherboard
The GPU gets to use memory from two sources. It prefers
the local "Video_Memory" because that has a very high
bandwidth. In the example above, I've shown a card with
512MB.
A second mechanism for the GPU, is shared memory from
the main memory space. The AGP bus features something
called an "Aperture". You can set the "Aperture" value
in the BIOS, and the value can be limited. It can be
limited by available system memory, but more likely,
doesn't work right when set too high. So the BIOS
may have a limited value in it, like 256MB as the
highest setting for the Aperture.
If you were playing a 3D game, the game would have a
total memory of (512MB + 256MB) to work with, for
storing compressed textures for example. When the game
first starts, it could be that only the 512MB section
is being used. The other portion is allocated as needed.
The AGP GART, maps allocated chunks of memory, in such
a way that they look contiguous to the GPU. The GPU
thinks it is getting one long continuous chunk of shared
memory, when it could be several pieces stitched together.
The AGP GART and aperture, work their magic to make that
possible.
http://en.wikipedia.org/wiki/Graphics_Address_Remapping_Table
When the GPU wants some of that shared RAM contents, it
uses DMA (direct memory access) or DIME (direct in memory
execution), to use the shared memory. If your drivers
are set up and all the hardware settings are OK, you can
see DMA/DIME enabled when reviewing the GPU config information.
There isn't anything of importance in that brief overview,
except to note that your BIOS does have an "aperture" setting,
and if you're getting a relatively "big" video card, like
your 512MB example, there is no real need to set the
aperture very big. You could set it to a nominal value
like 64MB. In some cases, there have been stability issues
with one particular setting value of the aperture, for
unexplained reasons. If you're using a modern video card,
with gobs of private memory of its own, then the only
thing you want from your aperture, is stability. You
don't really need to steal any system memory, even if
it is allocated dynamically and only when needed.
The biggest deal with buying modern AGP video cards,
is the quality of the drivers. Before you buy your
512MB card, read the reviews, and make sure you know
of at least one download site for a good driver. The
value of the card, is actually in the driver, and for
some cards, there might only be one "hotfix" driver
version worth having. If none of the customers have
been able to find a good driver for gaming, then it
is pointless to want one.
If you're using an older OS like Win98 or Win98SE,
the address space used by the video card can be an
issue for how much main memory the system can use,
and Windows remain stable. If you're using something
like WinXP, then you have nothing to worry about -
just find one stable driver, and you're done. Usually
the CD in the video card box, will have a copy of
..NET 2.0, a copy of DirectX 9c, or whatever other software
the video card needs. You may see more than one installer
run, when you install the card.
Don't forget to uninstall the previous video card driver,
before shutting down for the last time and physically
removing the old video card and installing the new one.
When your new screen comes up for the first time, it'll
run 640x480, while you install the drivers. After
a reboot, normal resolution options and 32 bit color should
again be available.
You can use a utility like this, to display the details
for your new video card.
http://www.techpowerup.com/gpuz/
If you want to benchmark "before" and "after", try 3DMark2001.
It is a relatively small download, compared to the other versions.
This'll give you some idea whether you got your money's worth
or not. You can run one benchmark now, and then run it again,
after the new card is installed.
http://www.majorgeeks.com/3Dmark_d99.html
Paul
