Help and UtilitiesAGP aperture size

Computer help and Utilities
Post Reply
User avatar

Topic author
Gen Stranger
|iog| Administrator
Posts: 241
Joined: Mon Jan 19, 2004 6:28 pm
Zodiac: Gemini
Contact:

AGP aperture size

Post by Gen Stranger » Thu Sep 20, 2007 10:36 pm

I decided to make this to allow others to help each other with computer problems

I will start it off with something that has been questioned of me and decided to see if I could find and answer.
What is AGP Aperture size?
Author: W1zzardDate: 2004-05-16 03:55:36

--------------------------------------------------------------------------------

How big should I set AGP Aperture size in my BIOS?

First of all, AGP Aperture memory will not be used until your video card's on-board memory is running low. That means it will usually not impact your gaming performance because developers are trying hard to not exceed the on-board memory limits.
The bigger your video memory, the smaller your Aperture Size could be. However with later games requiring more and more texture memory a good number seems to be 128MB Aperture Size for all cards with 64 MB to 256 MB Video RAM.
Setting the Aperture Size to HUGE values will not increase performance because this merely sets the maximum amount of physical memory that can be used. It only makes the GART Table bigger because every 4K page has its own entry, no matter if allocated or not.
Setting the Aperture Size to too small values could result in running out of available texture memory especially on a low-mem video card. It is also possible that developers make use of the GART's features by creating textures as 'non-local'.

If you experience in-game stuttering try playing with the size of your Aperture.

What is it from a technical point of view?

When using an AGP card the video memory on the graphics adapter is mapped into the 4 GB memory address space (above the region of the physical installed memory). Any accesses to this memory region are directly forwarded to the video memory, greatly increasing transfer rates. However in earlier days of video cards graphics memory was rather limited and ran out quickly (a single 32-bit 512x512 MIP-mapped texture consumes ~1.5 MB) so AGP added a mechanism to use the system's main memory as additional storage for graphics data such as textures. This is what the AGP Aperture is. Usually directly below the mapped video memory the system reserves a contiguous space of addresses the size of your Aperture (no physical memory will be consumed at this time).
When free video RAM is running low the system dynamically allocates 4K sized pages of system memory for use as AGP Aperture Memory. The problem with this dynamic allocation is that in many cases the pages are spread in a non-contiguous form throughout the physical memory. Accessing these pages directly would hinder performance because of scattering/gathering requiring extra logic. To get around this limitation the GART (Graphics Address Remapping Table) which is implemented in hardware in the Northbridge's Memory Controller Hub provides an automatic physical-to-physical mapping between the scattered pages and the AGP Aperture.
Gen Stranger
|IOG|-Stranger

User avatar

Topic author
Gen Stranger
|iog| Administrator
Posts: 241
Joined: Mon Jan 19, 2004 6:28 pm
Zodiac: Gemini
Contact:

and then this is this

Post by Gen Stranger » Thu Sep 20, 2007 10:48 pm

AGP Aperture Size
AGP aperture size (in MB) is memory that has been reserved from your system RAM for graphics processing. The size of the address space ranges from 4MB to 256MB and is configured in the BIOS and will most likely default to 64MB. In some cases, the system BIOS will allow the user to change it.

Intel recommends that the aperture always be set at 64MB even if the amount of actual system memory (RAM) is less than 64MB.
I personally set mine to the size of the memory on the video card
but after finding these articles I will start setting mine at 128 Meg
even though my card has 512 meg on it.
Gen Stranger
|IOG|-Stranger


SPUD

)

Post by SPUD » Fri Sep 21, 2007 4:20 am

I set mine as well to 250 mb the size of my card, so would it be better to lower the AGP slot to say a lower rate, i wonder? Looks like a test or two in order. Good article Gn wrthly

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest