>He explained that L2 cache was needed because there is not
>enough room on the cpu for any more L1.
Whoever told you that, is probably out of the loop for a looong time. L2 cache was off die, on the motherboard, in the Pentium 1 days, and earlier. Ever since the Pentium Pro/Pentium 2 it has been on the same CPU module, and since Pentium 3 and Pentium 2 Celeron A it has been ondie, so integrated on the CPU.
Level 1/2/3.. does not say anything on where it is located. The number just refers to its relative position in the cache hierarchy. L1 is closest to the core, typically smallest and fastest. L2 is typically bigger and slower, and 'further away' (both physical, distance, and in latency). L3 is even bigger, slower and further, etc. Some ISA's even have L4 caches, like on the chipset, and if you like, you could consider main memory (RAM) as a level 4 or 5 cache to cache your harddisk.
>Why not just make L2 cache bigger
because bigger typically means slower. Not too mention more expensive (diesize).
> I've noticed that AMD don't use it but Intel do
Intel includes L3 mostly only for its server chips. In multiprocessor configuration, you can never have too much cache, especially with shared bus topology like Xeon or Itanium. You'd typically have 2 or even 4 cpu's using the same memory controller and front side bus, so each cpu's bandwith is cut in half (or by four). To counter this, bigger caches help reducing the need to access main memory.
AMD uses a different approach with its opteron. using an ondie memory controller on every cpu (actually, two controllers per cpu), there is much less need to increase the caches as every cpu has its own memory controllers, and doesnt need to share them with 3 other cpu's. This allows it to access the RAM relatively fast (low latency), and with full bandwith. You could say main memory pretty much acts like a giant L3 cache on an opteron server.
>it pipelines the speed faster" before admitting he had no
>idea.
Exactly, he had no idea. Sounds like uou wasted your time on that lecture .
= The views stated herein are my personal views, and not necessarily the views of my wife. =
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