DDR RAM timings - what are the real performance boosters ?

[GreenBeret]

As some of you may know, I've done quite a few tests on CAS 1.5 vs 2.0 vs 2.5 in this thread: http://www.xtremesystems.org/forums/showthread.php?s=&threadid=3849

I concluded that CAS doesn't affect performance much, if at all (at least on my P4 rig anyway). I observed that the difference in 3DMark between 2.5-6-3-3-enhance off and 2.5(2)-5-2-2-enhance on is about 350 points, so I had a thought: the real performance boosters are among: RAS to CAS, Ras Precharge, TRAS, and Enhance DRAM performance (aka DRAM Idle timers = 0 on some boards).

So today I did a few quick 3DMark tests at 220Mhz RAM. I tested with enhance on and off, and Ras to Cas =2, then 3, and Ras Precharge, and TRAS = 5,6,7.

My observation:

- Enhance ON (or DRAM Idle time = 0) gives about 50 points, I can notice the fps increase a little bit at certain spots, but not very significant, I must admit.

- Tras: no difference at all.

- Ras to CAS delay: This one is amazing ! I got 150 points increase straight away ! Got about 6~8 fps (sometimes even more than that) in all CPU-memory intensive tests at certain spots (you 3DMark gurus know what they are ;) ).

- Ras Precharge: unfortunately, my RAM can't handle this setting at 220MHz (Samsung CTL). However, from the difference between 2.5-6-3-3 enhace off and 2.5-5-2-2 enhance on that I posted above, you can subtract what Enhance and Ras to Cas give, and you can see that Ras Precharge may give even more performance increase than Ras to Cas Delay. Can someone with better ram than mine test that please ? Thanks a lot :)

What do you think ? :)

[N8]

I have not fully tested but I can verify that your theory on the Cas is not true of AMD rigs. I didn't write numbers down while testing it, but I lost quite a few points by going from Cas2 to Cas2.5. In my experience(not really verified, just as I remember it) CL, Interleave, & Command Rate were the big ones on my AMD rig as far as Sandra/3DMarks are concerned.

[Marci]

And on AMD rigs, all I see Enhance do is add 1Mhz to the mem frequency...

[GreenBeret]

Originally posted by Marci
And on AMD rigs, all I see Enhance do is add 1Mhz to the mem frequency...

Enhance DRAM Performance is a term invented and used only by Abit. They are different on Intel and AMD boards.

On other Intel boards, it's DRAM Idle Timer = 0 T (other choices: 8T, 16T, 64T, Infinity).

I"m not sure what it really is on AMD boards though.

Can anyone with P4 & DDR verify what I observed ? Thanks :) AMD + DDR is welcome too :) Check what RAS to CAS and RAS Precharge do to your system performance.