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Subject: Re: New G4's; ddr L3 cache significant or not?

Author: Vincent Diepeveen

Date: 08:50:13 01/28/02

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On January 28, 2002 at 11:44:00, Will Singleton wrote:

>The new Mac G4's came out today, 933mhz and 1ghz versions.  Question: this 2mb
>of ddr L3 cache seems new.  Is that something that would significantly affect
>integer performance?

the slow speed of the processors, 933Mhz is the bottleneck here.

Also it is unknown what the penalty is for a branch misprediction. on
paper they can do like the P4 (which runs 2.2Ghz by the way) 4 instructions
a clock, but if branchmisprediction penalty is according to that, then
there is no fun here.

After this the L1 cache is real important. A bad L1 cache can do more harm
to a processor than L2 cache obviously can. L2 cache is for example
for crafty not relevant whether it's 1 MB or 2 MB (Xeon processors)

After L2 cache there comes the L3 cache.

So the importance of L3 cache is there of course, otherwise it would
not exist i guess. But a bigger L3 cache will not be like 20% faster or so
for a chessprogram. I doubt 1% even.

>Seems like the limiting factor is that old system bus again.
>
>- 256K on-chip L2 cache running at processor speed
>- 2MB DDR SDRAM L3 cache per processor, with up to 4GB per second throughput
>- 133MHz system bus
>
>Will



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