PCI-E Bus Over clocking

By HMJ

Virtualjesus23@mail.com

     The other day while scouring my bios for some random item I found a rather nostalgic setting that took me back to the good old days when I used an AGP video card.  This setting was the PCI-E bus frequency.  In this little menu you have the option of taking your standard 100 MHz PCI-E bus and increasing it to upwards of 145 MHz, many motherboards may not have this option or even if they do they may not have the capacity to push up to 145 MHz.  In an old AGP system while increasing the AGP Bus one or two MHz over its native 66 you would receive a decent performance boost unfortunately you could only ever push the bus up 3-5 MHz before the whole system would crap out.  Using this knowledge and the knowledge that new PCI-E video cards can take much more stresses than older cards I endeavored to raise my PCI-E bus in the hopes of gaining performance similar to the fashion of older AGP boards.  This is what I came out with:

             Starting with a single MHz increase in bus speed I decided to gauge any potential performance increase with a standard set of synthetic benchmarks including Aquamark3 and 3dMark05.

My tests utilized an AMD Athlon 64 3000+ Venice, DFI Lan Party Ultra-D, Thermalright XP-90 A, 2*512 Crucial Ballistix DDR 400 2-2-2-5 1T, ATI X850 XT.

Synthetic Benches

*Aquamark3 run at 1024*768*32Bit, AA-Off, AF 4x, Very High Detail

** 3Dmark05 run at 1024*768*32 Bit

     Needless to say that based on my history with AGP cards these were not the numbers I was expecting to garner.  Based on these numbers I could have made an early conclusion that on PCI-E cards increasing the Bus MHz has little or no discernable effect but I decided that would be a bit of a hasty decision. So to test my little theory I decided to bring out the big guns; you guessed it real, world game tests.YAY!!!

     In order to test once and for all if PCI-E bus over clocking is capable of being used as a performance enhancing measure I decided to test it against some of the hardest game benches available; Doom III, and Half Life 2

Game Benches

* Half Life 2 run at 1024*768*32 Bit highest detail

** Doom III run at 1024*768*32 Bit AA 4x, High Detail

     Once again not what I was expecting but eh what can you do, the facts are the facts. As for why, I have no idea why the PCI-E bus does not function in the same way the old AGP bus did. Perhaps modern PCI-E graphics cards are incapable of using more bandwidth than they receive at their native 100MHz bus or maybe they are hardware locked from being able to accept a bus over clock for stability reasons.  Whatever the reason maybe over clocking your PCI-E cards bus speed will not gain you performance and if youre looking for a way to increase your video performance this isnt it, but at least now you know.

 : Note: I would have been interested in getting performance numbers for an AGP card and bus but none were available at the time I wrote this article.  Additionally, I would have loved to be able to test a NVIDIA based card to see if there cards were affected by PCI-E bus over clocks, but I doubt it.

 HMJ