ATI Memory Speeds...can anyone explain?

[Joe DeFuria]

After seeing this chart in another thread:

Something just struck me as odd, and I was wondering if anyone had a technical explanation.

Why is the ram consistently clocked "just under" the core clock? One would think that generally, it would be more efficient to synchronize the clocks. I could see the argument being made that puching mem clocks higher on the 9700 Pro may cause unacceptable stability issues, but why would the 9700 non-pro and 9500 mem clocks be at 270 Mhz, instead of 275? I can't see any economical or stability reasons for it, so I presume there is a technical one....

Anyone?

 

[arjan de lumens]

The only reason I can think of offhand would be EMI - with everything running at the same clock speed you get a rather large spike of noise at one frequency - running core and mem at slightly different clock speeds may result in two smaller spikes instead. This is just a wild guess, though - there may be other possible reasons that I am not aware of.

 

[demalion]

Actually, I thought it likely to be a simple typo cut and pasted, as I thought other reports indicated 275/275 for both. Could be that it simply changed, but the typo option seems more likely to me until more info comes out.

 

[arjan de lumens]

Looks like a typo alright - hardware.no, who supplied that table, refers to Chip Online (chip.de) as their source, but the chip.de table states 275/550 MHz for all the 9500/9700s except the 9700pro.

 

[K.I.L.E.R]

Is that possible?

The only reason I can think of offhand would be EMI - with everything running at the same clock speed you get a rather large spike of noise at one frequency - running core and mem at slightly different clock speeds may result in two smaller spikes instead. This is just a wild guess, though - there may be other possible reasons that I am not aware of.

 

[Pete]

If it was a typo, this will be the shortest-lived conspiracy I've seen.

 

[JF_Aidan_Pryde]

Which makes me wonder, why didn't ATI use 325Mhz memory for the 9700 PRO?

 

[Dave Baumann]

Supply. They are having enough trouble even getting enough 310MHz.