AGP speed mystery

[Offler]

I was testing some things on my machine and now i am completely confused.

Theory says that if the AGP speed is higher the graphical performance is better.

In real world i can set speed of AGP slot from 4x, 2x, 1x or completely disable all acceleration to run the graphics on PCI bus speed.

It doesnt matter what AGP speed i choose, system performance is affected only when i turn off AGP completely.

Question:

Am i running on agp 1x or agp 4x or the bus is not fully utilised?

System configuration:

Board: Abit VH6-T

Pentium III 1,13 Tualatin

Ati Radeon 9800 Xt 128 Mb

I tried dos based app called VSpeed to measure real speed of AGP bus. I reached number 500mb/s which is speed close to agp 2x. On higher speeds the app failed to measrue because it showed numbers like -300 mb/s.

Answer 1: System test shows that i am running at least at AGP2x, but real applications shows that the AGP utilisation can be much lower (133-266 mb/s which is speed of AGP1x)

Queston2:

Why is capacity of AGP slot not utilised?

I tested same HW with windows 2k. no change in behaviour, so OS is not the reason, but i used same drivers as in win98. In w2k was vspeed unable to measure any activity around graphics data channels. I also measured that no HW component (except cpu or gpu) could affect agp utilisation.

At this point i failed to find any reason why the theoretical bus speed is far from real data streams, even when the applications (prey, oblivion) are able to utilise it...

Question3 (for the public here )

Did someone of win98 users encounter this? It is very strange behaviour and it makes no sense to me. There is possible that CPU or GPU are the limiting factors, but there is also possible that some part of system is affecting AGP functionality in negative way by lowering the real data stream.

[galahs]

I have read in many instances that the real world speed differences between AGP ports is very minimal.

usually because the bottleneck in the system is elsewhere CPU, system ram, gpu etc

[Fungus]

The AGP speed only affects how fast the textures and other data are initially loaded into the card, once the data is in the card's ram, there is little or no difference.

also, the Abit VH6-T board of yours is known to have "bad capacitor" syndrome, you might want to check your capacitors and make sure none of them are bulged or leaking.

I also have a bios for that board which supports the SL6BY 1.4ghz tualatin (TB-1 stepping). Let me know if you want it.

[Offler]

Ram or chipset in this case is surely not a bottleneck. If there is a bottleneck it can be only gpu and cpu, no other component. Maybe the Video ram is really large enough to keep all data necessary for apps.

Capacitators are ok here. I bought this board few months ago. it was used with coppermine 900, so i put there Pentium III 1,13 and overclocked it. Since i use very good PSU i can say that no leaking here occurs. I can safely lower cpu voltage from 1,475v default to 1,125 even when it is overclocked and the system works (temperature is very low, when in room was 20 degrees, on cpu was 22 degrees with air cooling )

Bios has been modded by modbin utility som i have done some minor changes in it.

I am looking for new cpus, like 1.4 tualatins with 512kb cache

btw what is the difference between TA1 and TB1 steppings?

What kind of bios you mean? i use newest bios with some home made mods.

[Fungus]

You'll have to consult intel tech manuals on the differences between the steppings, I am not that techie

All I know is proc with TB-1 stepping will not work with standard bios. You have to add microcode to support that. I friend of mine has done this to his bios, and gave it to me in case I ever run across one of those boards. They are quite rare.

[Offler]

Abit VH6-T is quite masterpiece. They still use SDram as most boards of this type, but the memory and bus efficiency is extremely high - 97% ( if we compare real memory throughtput to theoretical memory bandwith), so if i can theoretically read from RAM 1264 mb/s i am able to read 1214mb/s.

Few SDRam and even DDRam based boards are able to reach such efectivness. Thats why i have chosen this board as basement for the rest of system - win98 based