So ok i understand the Concept of AGP aperture.. but is the aperture
software coded? or is it a Hardware setting like a certain chip? i.e.
my max AGP aperture is 256... can i make it go to 512 if i had a BIOS
update?
I was just wondering cause i just bought a new 512 nVidea 7600 agp
my motherboard from Intel is no longer being updated (yeah yeah old
mobo, D875PBZ) but its not really THAT OLD..
thanks for the help if any .. =/
Part of the purpose of an AGP aperture, is to use system memory as
an extension of the video card memory. It allows some operations
(texture transfers perhaps), to move information at high speed,
from distributed bits of system memory, to or from the video
card.
If your video card has 512MB of real video memory, then a 64MB
(trivially sized) aperture would be fine. The card will pretend
it has access to a max of 576MB.
The purpose of the aperture, is to map bits of memory, into a
contiguous chunk. Say the aperture is set to 64MB. And say the
aperture address translation had 64 slots. The operating system
allocates memory on the fly. When the OS starts, no memory is
being accessed through the aperture.
Say a game needs 513MB of textures. The OS goes to system memory,
and takes 1MB out of service. It goes to the GART, and maps a
1MB segment to one end of the aperture.
10 minutes later, the game happens to need another megabyte of
texture storage. The OS goes to system memory, and gets a
second 1MB chunk. It happens to be physically far removed from
the first chunk.
By the magic of the GART, to the video card, the two 1MB pieces
are addressed physically contiguously (the GART translates a physical
address, to a different physical address). When the video card DMA
transfers textures, as it steps over the 1MB boundary at the
bottom of the aperture, it doesn't even notice that the physical
memory is quite "far away" from the other chunk.
In summary:
1) The aperture represents a reserving of address space.
The larger the aperture, the less address space for other things.
This affects people with 32 bit OSes, who have plugged in 4GB of
memory into their AGP based systems. The larger the aperture, the
less physical memory will be reported in Windows. If aperture is
64MB, maybe they see 3.25GB. If aperture is set to 512MB, they
would then see about 2.81GB. Setting a high aperture, is really
only an issue for someone with 4GB of memory, and other people
won't care. Address space is only an issue, if you've run out of
address space.
2) The aperture doesn't do anything until needed. If no game is
being played, then no system memory would be allocated to the aperture,
and there would be no entries in the GART table. In other words,
setting the aperture in the BIOS, does not immediately use any of
your precious system RAM.
And with your 512MB video card, it is possible, that even when a
3D game is being played, the aperture still isn't being used.
3) Allocation is dynamic. Stuff can be added or subtracted to the
GART, at the OSes discretion. When a game is finished, the mappings
in the GART could be removed. It is all up to the software that
manages the GART, as to what exactly happens. (I'm not a software guy.)
Since the aperture is an *extension* to the 512MB of memory on the
video card, you've already got enough, and making the aperture
bigger really isn't necessary.
Note - this is my understanding of it. If you want to read some details,
try page 116 section 5.3 "AGP graphics aperture" of this document:
http://web.archive.org/web/20030314...m/technology/agp/downloads/agp30_final_10.pdf
Paul
