AGP Graphic Aperture Size?

[oc jason]

It is set to 32 in BIOS and i have the choice for 64 and 256. Would any of these setting make a difference if i have 256 megs of phyical memory installed?

[Da Whip]

Most will tell you to set it to 64. I have followed that advice and it seems to work well .

[Jon]

I've always set it to half my onboard memory. I have 256MB so I set mine at 128MB.

64MB will probably work just as well as any...I've never run any tests to see if there is a performance difference.

[Mac42]

It really depends on how much video memory you have... the more video memory you have the less graphics apeture you actually need. You shouldn't ever need anything higher than a 64Mb apeture, but if you have a card with 32Mb or 64Mb you could lower your apeture to 32 or 16. People have run some benchmarks and there's not really much difference either way. 32 or 64 should be fine even with 256Mb of system ram.

[o770]

take a look at here to understand everything about AGP ap size:
http://www.rojakpot.com/Speed_Demonz/BIOS_Guide/BIOS_Guide_02c.htm
scroll down till the AGP ap size.

[Placid]

AGP Aperture Size (MB)

Options : 4, 8, 16, 32, 64, 128, 256

This option selects the size of the AGP aperture. The aperture is a portion of the PCI memory address range dedicated as graphics memory address space. Host cycles that hit the aperture range are forwarded to the AGP without need for translation. This size also determines the maximum amount of system RAM that can be allocated to the graphics card for texture storage.

AGP Aperture size is set by the formula : maximum usable AGP memory size x 2 plus 12MB. That means that usable AGP memory size is less than half of the AGP aperture size. That's because the system needs AGP memory (uncached) plus an equal amount of write combined memory area and an additional 12MB for virtual addressing. This is address space, not physical memory used. The physical memory is allocated and released as needed only when Direct3D makes a "create non-local surface" call.

Win95 (with VGARTD.VXD) and Win98 use a "waterfall effect". Surfaces are created first in local memory. When that memory is full, surface creation spills over into AGP memory and then system memory. So, memory usage is automatically optimized for each application. AGP and system memory are not used unless absolutely necessary.

Many people recommend the AGP aperture size should be half of the amount of RAM you have. However, that's wrong for the same reason why swapfile size shouldn't be 1/4 of the amount of RAM you have in your system. As with the swapfile's size, the AGP aperture size required will be smaller as the graphics card's memory increases in size. That's because most of the textures will be stored on the graphics card itself. So, graphics cards with 32MB of RAM or more will require a smaller AGP aperture than graphics cards with less RAM.

If your graphics card has very little graphics memory, then you should set as large an AGP aperture as you can, up to half the system RAM. For cards with more graphics memory, you shouldn't set the aperture size to half the system RAM. Note that the size of the aperture does not correspond to performance so increasing it to gargantuan proportions will not improve performance.

Still, it's recommended that you keep the AGP aperture around 64MB to 128MB in size. Now, why is such a large aperture size recommended despite the fact that most graphics cards now come with large amounts of RAM? Shouldn't we just set it to the absolute minimum to save system RAM?

Well, many graphics card require at least a 16MB AGP aperture size to work properly. This is probably because the virtual addressing space is already 12MB in size! In addition, many software require minimum AGP aperture size requirements which are mostly unspecified. Some games even use so much textures that AGP memory is needed even with graphics cards with quite a lot of graphics memory (32MB).

And if you remember the formula above, the amount of AGP memory needed is more than double that of the required texture storage space. So, if 15MB of extra texture storage space is needed, then 42MB of system RAM is actually used. Therefore, it makes sense to set a large AGP aperture size in order to cater for every software requirement.

Note that reducing the AGP aperture size won't save you any RAM. Again, what setting the AGP aperture size does is limit the amount of RAM the AGP bus can appropriate when it needs to. It is not used unless absolutely necessary. So, setting a 64MB AGP aperture doesn't mean 64MB of your RAM will be used up as AGP memory. It will only limit the maximum amount that can be used by the AGP bus to 64MB (actual usable AGP memory size is only 26MB).

Now, while increasing the AGP aperture size beyond 128MB wouldn't really hurt performance, it would still be best to keep the aperture size to about 64MB-128MB so that the GART table won't become too large. As the amount of onboard RAM increases and texture compression becomes commonplace, there's less of a need for the AGP aperture size to increase beyond 64MB. So, it's recommended that you set the AGP Aperture Size as 64MB or at most, 128MB.

http://www.rojakpot.com/Speed_Demonz/BIOS_Guide/BIOS_Guide_02c.htm

[oc jason]

thanks guys i have 64mb AGP mem. so ill set the BIOS for 64 MB aperture size as i just got another 1268mb system mem.

[samuknow]

I actually set it to max. I seem to get the best stability this way. Maybe it's just my mobo. I know it doesn't slow down my system. Seems to help when ocing my vid card.


My suggestion is to try a few different settings and see what works best for you.

[o770]

i also set it up to 256MB. cant remember where did read a recommendation to set it this way but i beleive it can be good for most the systems. higher the amount of aperture u give to the AGP more detailed graphics will be released to the vid card render. 64MB is enough for most the applications but in some cases it wont be enough to run the 64MB texture test in 3dmark2000 for ex. benchmarking with both showed me theres almost no loss in performance setting it up to 256.

GeForce II MX 32MB
128MB RAM
W98SE
DirectX 7a

[asmodean]

I'm keeping my aperture at 256mb too. I've 384mb memory & 32mb on vid. card. Dunno if it helps or not.

[barre]

i ran some tests and the diff was 1 (read: one) mark in 3dmark2k between 4mb and 256mb of agp aperture. i don't know if this is a general thing. i only ran the tests twice for each setting so i can't say if there is any diff. in stability, neither of the settings caused any probs. otherwise i use 64mb (i have 16mb vid card memory)

[samuknow]

I don't imagine that the tests will differ much. I run max for stability issues. Espically when OCing my Vid card. Again, I'm sure results will differ with mobo's and hardware.