Why did my RAM performance decrease when I added more identical sticks?

[Glendor]

I'm still trying to test this out, but here's what it seems like:

Fatal1ty AN8-SLI mobo
Opteron 165 (no OC)

4x 512mb Corsair DDR400 (cas 2.2.2.5)


I ran MemTest several times making sure the memory didn't have any problems, and there is a speed rating on the screen. I can't remember the exact numbers, but you'll get the picture (I hope):

2x512mb = 2250(k/sec? m/sec? whatever/sec!)

but

4x512mb = 1700 ???

I noticed a similar trend in SiSoft Sandra, but I'm even more vague about the exact numbers.

What's going on? Adding more sticks of identical memory causes performance to decrease? Is this normal, or am I doing something wrong?

Glendor...

 

[Ruptga]

Early K8 chips would revert to DDR333 instead of 400 when four sticks were used, identical or otherwise. I believe that has been fixed for a little while, but memory performance will always drop when going from two sticks to four, it's just harder to get four sticks to match up, and you have to go with the slowest of the four, so any one crummy stick will slow down three excellent sticks.

Like I said, I think the bandwidth issue with AMD's IMC has been fixed for quite a while, but you can still expect latencies to suffer, though I don't know by how much or if it's noticable without a benchmark (I'd be surprised if it is, memory latency isn't that important in the grand scheme of things, maybe makes 1-4% of a difference.)

 

[Glendor]

If I check and find out my DDR400 is reverted to DDR333, is it recommended that I manually set it back for DDR400?

Any other suggestions?

Glendor...

 

[drakore]

ummm when u have 4 sticks on an amd machine you lose 1t timings which is a big performance hit.

manually set it to ddr400 in the bios

 

[aka1nas]

Originally posted by: Glendor
If I check and find out my DDR400 is reverted to DDR333, is it recommended that I manually set it back for DDR400?

Any other suggestions?

Glendor...

Any of the dual-core AMD chips are at least revision E and support 4 sticks@200Mhz. Most boards will still default the RAM speed down anyway, it should be fine to manually set the speed. You cannot run 1T command rate with 4 sticks 99% of the time.

 

[Glendor]

I got my Fatal1ty board back from Abit RMA and retested it with Sandra

4x 512mb 2.2.2.5 gets a Latency score of 92 ns and a speed factor of 52.3

I wish I has written down the exact Sandra scores from before so I would have something to compare to. That seems like a better score though.

What do you think?

 

[Yellowbeard]

Set it back to DDR400 manually and test it for stability. Also, set your memory voltage to the 2.7v to 2.9v range if needed. 2.9v is max for warranty. If it is stable, I would not worry with any artificial benchmarks or scores. The command rate change from 1T down to 2T will cause a drop in benchmarks but, you cannot detect the difference with the naked eye or real world usage.

 

[Yellowbeard]

Delete, Double Post.

 

[tw1164]

I have a 3800x2 w/ a A8N-SLI board. I had to manually set my mem speeds when I moved from 512mb x2 to 512mb x4. I didn't need to bump up the voltage though.