AGP Aperture Size?

[ConLog]

My AGP Aperture Size in the BIOS is set at 64MB. I have a 128MB Graphics card and 256MB of memory.

Do I need to change the AGP Aperture size?

[Furius92]

I think it is good to have an AGP aperture size that is twice the amount of memory on your video card. For you, that would be 256MB, but I haven't seen anything higher than that on any BIOS. I believe the AGP aperture size deals with the amount of data that is cached before being sent to the card, or maybe if the card's memory fills up...

[shifty]

It's an interesting question an one I don't hear much about.One formula I've heard of is to divide the video card memory in half and then divide that into the system memory.An example would be if you had 64mb video memory and 256mb system memory you would divide 256 by 32 and that would be an 8mb aperature size.I have my system set to that and it seems to run better than the default 64mb.I hope some of the more knowledgeable guys could post about this.

[ConLog]

Thanks. Interesting replies!

Most motherboard manuals don't carry any info about the mysterious "AGP Aperture Size".

[shifty]

Check out the web sight www.lostcircuits.com.Look at bios 101 for bios settings.

[shifty]

www.lostcircuits.com

[Lord Prism]

"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.
Many people recommend the AGP aperture size should be half of the amount of RAM you have. 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/

Try different setting and see what gives you the best performance.
Mine is set to 128 and I get best performance there.
XP1800+, 768MB PC2100, Ti4600 128MB.

Good Luck,

[shifty]

now it's all clear

[Markoman01027]

I have a 64MB card. Should I set it at 128MB or keep it at 64MB? it's set at 64MB right now. Would I still add the +12 ?

Nevermind. It was set at 128MB. Disreguard my message.

[Force Flow]

Taking the question from Markoman01027, I'd like to know if there would be a performace increase by increasing the apature from 64MB to 128MB with a 64MB card.

For example, would there be less time where there is lag in a game while viewing an area with a high number of polygons?

[Markoman01027]

Good question Force_Flow. Kinda wondering that myself.

[Lord Prism]

Try 64 then 128 settings and see what gives you the best performance.

[TwoRails]

Originally posted by force_flow2002 Taking the question from Markoman01027, I'd like to know if there would be a performace increase by increasing the apature from 64MB to 128MB with a 64MB card. For example, would there be less time where there is lag in a game while viewing an area with a high number of polygons?

From everything I've read, the answer is no.

My BIOS book is in PDF format, and it's locked so I can't cut-n-paste it's section on this, but it's fairly close to the above. (anyone know how to unlock a PDF?)

TwoRail

[Force Flow]

You could try taking a screenshot and attaching the file here.

[TwoRails]

OK, here's the screen shot:

TwoRails

[Force Flow]

Ah. So I guess it's another case of "if it's not broken, don't fix it."

[TwoRails]

I guess so! I've played with the settings, but never benchmarked them, and never noticed a difference. With today's CPU and GPU speeds, it probably matters even less than when 16MB vid cards were "big."

TwoRails

[GSXdan]

Well, I decided to do some benchmarking and here are my results:

64mb aperture size: 10983 3d marks
128mb : 10838 3d marks
256mb : 10803 3d marks

This is with a ATI Radeon 9500Pro 128mb DDR vid card. See sig for other specs. I guess id like to see some other results, so if anyone wants to try it, post your results here.

^dan

[TwoRails]

Nice post, GSXdan! No wonder I never saw a difference. There virtually is none!

TwoRails

[GSXdan]

Yea, I played the same game(Test Drive) under each setting and there was no noticible difference, so I guess keeping it at 64mb is fine.

^dan