AGP aperature?????

[darrelld]

Can anyone explain what this is and how the setting affect performance?

[OPPAINTER]

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.

The size of the aperture does not correspond to performance so increasing it to gargantuan proportions will not improve performance. Many graphics card, however, will require a larger than 8MB AGP aperture size to work properly so you will need to set a minimum of 16MB for the AGP aperture size. Even then, you should set the aperture size at a higher setting so that it will be large enough to accommodate any texture storage requirements that your games/applications may have.

At the moment, the rule of the thumb is an AGP aperture size of about 64MB to 128MB. Increasing the AGP aperture size beyond 128MB wouldn't really hurt performance but it would still be best to keep the aperture size to about 64MB-128MB so that the GART table won't be 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.

[ecryptic]

I have a 32 meg AGP GeForce2 video card, via motberboard, AMD athlon 1 GHZ CPU. My System would lock up in the middle of playing games, I set this option from 128 to 4 to test it, I saw no difference in proformance, but I didn't get this lock up. I need to test it more, but I think 64 also prevents this. Is there any danger in setting it too high? My system would freeze all the time when AGP 4X was on, btw, what is AGP 4X? What does it do on vs off?

[Dudster]

Hi ecryptic http://www.sysopt.com/forum/smile.gif

Setting your aperture to 4 will actually disable AGP acceleration (as will anything below 32) so it'll be like a PCI card. Have a look here for more info www.geforcefaq.com/faq.cgi#hw:gef:agpapset (http://www.geforcefaq.com/faq.cgi#hw:gef:agpapset) If you can get 64 running ok, I'd use that. I've got 256MB of RAM and set mine to 128 which never locks-up (well not since I replaced my poor quality generic PC100 CAS3 RAM anyway).

AGP 4X is the speed/bandwidth of the AGP bus (I think AGP 1X is 33MHz). There isn't much difference in performance between 2X and 4X. www.geforcefaq.com/faq.cgi#hw:gef:troub:mbc:viaagp4xstable (http://www.geforcefaq.com/faq.cgi#hw:gef:troub:mbc:viaagp4xstable) This might help you with your 4X problems. Again, mine is set to 4X with Fast Writes and SideBand Addressing enabled but I have a GeForce 256 (Via KT133 chipset).

[ecryptic]

Does sidebanding and fastwrites help peformance that much? I need to get the fastest performance for my 3D modeling.

[NDD]

Enabling SBA and Fast Writes gave me about 200 extra points in 3DMark2001, using Leadtek WinFast GeForce2 GTS 32MB DDR revA.
Having them enabled is not so critical, it's merely 3-5 FPS in real games.

Best Regards ...

[Dudster]

I only enabled SideBand Addressing on my GF256 SDRAM recently after reading this www.rojakpot.com/Speed_Demonz/AGP_Sidebanding/AGP_Sidebanding_01.htm (http://www.rojakpot.com/Speed_Demonz/AGP_Sidebanding/AGP_Sidebanding_01.htm) (I've always had Fast Writes enabled)

I gained about 10 points on the default 3DMark2000 benchmark and lost the same on the default 3DMark2001 benchmark. I gained about 1FPS in Quake3 so decided to leave it enabled.

I think Sideband Addressing enabled is generally faster but it can be slower for some things and might cause some problems when enabled (you'll just have to test/benchmark everything with it enabled. Any problems, just disable it again).

Fast Writes probably gives a bigger boost than SBA but I'm not sure if the application/game has to support it or whatever. Again, you'll have to test your system with it enabled and disable it if it causes problems.

So, I'd recommend trying to get Fast Writes enabled before you try enabling SideBand Addressing (then you also know which one, if any, causes you problems).

P.S. AGP 1X is actually 66MHz http://www.sysopt.com/forum/smile.gif