Differences between L1 and L2 caches on P4 and Athlon XP Barton

[Link19]

I read that the Pentium 4 has 8 KB of L1 cache and the Athlon XP has 128 KB of L1 cache. I see that on their modern CPUs, they both have 512 KB of L2 cache. How important is the amount of each L1 and L2 cache on the CPU to overall system performance?

Does the RAM speed have to be equal to the FSB speed, or is it ok if the RAM MHz speed is different?

 

[TROGDORdBURNINATOR]

The athlon XP doesn't duplicate the L1 cache's data into L2 cache. If it did, then the 64 trace and 64 data cache would eat up 128K of a 512K cache and leave you with only 384K to actually use. The Pentium 3 and Pentium 4 do this although they have less l1 cache. The Athlon's cache is exclusive meaning that you actually have 640K of useable cache while with the P4 you have about 512K. Of course, the P4 cache has twice the width and is clocked much higher for the same PR rating of Athlon processor.

 

[Chobits]

What he said though being clocked higher is just different architectures because the Athlon XP has a higher IPC.

Lone Live the Epia!

Usually I'd say AMD or Intel but I'm starting to feel sorry for this processor- if only it could be more competitive with a Celeron I would seriously consider the purchase of it

 

[imgod2u]

Erm, inclusive doesn't mean you *loose* the cache space. So the P4 would have 512KB of total cache space available (the L1 is duplicated in the L2). There is a ton of differences.
As for the difference, the two MPU's caching systems are dramatically different. The P4 has no L1 instruction cache per se. It has an execution trace cache which store already decoded micro-ops vs the Athlon's L1 instruction cache which stores x86 instructions fetched from memory. The P4's L1 data cache is 8KB in size but with 1 cycle access latency and pretty massive bandwidth.
The P4's inclusive caching system means that the L1 data cache will be duplicated onto the L2 cache so it has 512KB of total cache to devote to data and pre-decoded instructions. The Athlon has 640KB of space to devote to this.

 

[TROGDORdBURNINATOR]

Yes, actually that's correct.

 

[AgaBoogaBoo]

I wouldn't try to really compare those two different CPU's because each of them benefits differently from added cache than the other.

 

[AgaBoogaBoo]

In regard to your last question, it is fine if the RAM isn't running the same speed as your FSB but remember that when there are memory intensive situations, that will become a bottleneck, for everyday usage (Not gaming), you probably won't notice a large difference, if any.

 

[Link19]

Chobits:

You are starting to feel sorry for what processor?

AgaBooga:

So are you saying that if you do memory intensive things, then the RAM speed should match the FSB MHz speed to avoid a bottleneck?

 

[AgaBoogaBoo]

Originally posted by: Link19
Chobits:

You are starting to feel sorry for what processor?

AgaBooga:

So are you saying that if you do memory intensive things, then the RAM speed should match the FSB MHz speed to avoid a bottleneck?

Yes, when you start to do RAM intensive operations, you should match the FSB speed so that the CPU can get as much bandwidth as possible.