Athlon's L1 Cache vs. Pentium's

[tguzella]

i've been wondering: athlon xp has got 128 kb of L1 cache (64 kb for code, and 64 for data, right??), while the pentium 4 has something like 16kb total... is athlon's cache slower?? i just can't believe both caches have the same speed...

 

[Mephistopheles]

They use different cache architectures, maybe there's something that makes the difference there...

I know just bits and pieces about that... What I know is that Athlon's cache is exclusive, meaning that the L2 cache contains different data than L1 cache; and P4s use inclusive caches, meaning that L2 contains a copy of L1 cache... L1 is much faster (several dozen gigabytes every second throughput). Now that alone probably doesn't really mean a lot for speed; anyway, both have access speeds that match the clock rate of the processor. Meaning that a P4 3.0Ghz has an "effective bus" of 3Ghz for its cache. That is why a 3.2Ghz probably takes a lot of benefit from a 2MB cache at 3.2Ghz access speed...

<font color=red><b>M</b></font color=red>ephistopheles

 

[imgod2u]

Yes, the Athlon's L1 cache is slower. In fact, for FP data, the P4's L2 cache is about the same speed as the L1 data cache on the Athlon.
Basically, the P4's "L1" caches shouldn't even be considered L1 anymore, more like L0 (yes, those are the registers technically, but I can't very well do L0.5 can I?). The instruction trace cache is part of the core itself, designed into the micro-architecture. The data cache is only there to store integer data. It gets all of its FP data from the L2.

"We are Microsoft, resistance is futile." - Bill Gates, 2015.

 

[Parhelia]

tomshardware posted a topic on cpus, and in it he explained the l1, l2 and l3 cache.and he put the differences between the caches of amd and intel. but im searching on it again and i lost it, i don't now wich one exactly.
But the test shows that the caches of the athlon64 is more than two times faster than those of p4 ones. And he told that thats ONE of the things that made athlons processor faster than intel ones at the same clock speed. Its one advantage of many.

<P ID="edit"><FONT SIZE=-1><EM>Edited by Parhelia on 10/12/03 03:42 AM.</EM></FONT></P>

 

[imgod2u]

tomshardware posted a topic on cpus, and in it he explained the l1, l2 and l3 cache.and he put the differences between the caches of amd and intel. but im searching on it again and i lost it, i don't now wich one exactly.
But the test shows that the caches of the athlon64 is more than two times faster than those of p4 ones. And he told that thats ONE of the things that made athlons processor faster than intel ones at the same clock speed. Its one advantage of many.

<A HREF="http://www.aceshardware.com/read.jsp?id=60000258" target="_new">Note the difference</A> between the L2 cache bandwidth.

"We are Microsoft, resistance is futile." - Bill Gates, 2015.

 

[Mephistopheles]

So P4s L2 cache has much more bandwidth than AFX's... as expected, actually, because these things work at clock speeds... It can also be seen that A64's on-die memory controller is a very strong advantage...

<font color=red><b>M</b></font color=red>ephistopheles

 

[Parhelia]

yeah ur right about the l2 cache, but in the latency benchmark and the sse2/mmx benchmark, AMD64 realy shines, and a lot. I was confused between the latency and the cache speed when i told my previous speed, now i remember.