Electronic – Why is L1 cache faster than L2 cache

cachecpumemory

I'm trying to understand why certain CPU cache memories are faster than others. When comparing cache memory to something like main memory, there are differences in memory type (SRAM vs DRAM), and locality issues (on-chip vs having to traverse a memory bus) that can affect access speeds. But L1 and L2 are generally on the same chip, or at least on the same die, and I think they are the same type of memory. So why is L1 faster?

Best Answer

No, they're not the same type of RAM, even though they're on the same chip that uses the same manufacturing process.

Of all the caches, the L1 cache needs to have the fastest possible access time (lowest latency), versus how much capacity it needs to have in order to provide an adequate "hit" rate. Therefore, it is built using larger transistors and wider metal tracks, trading off space and power for speed. The higher-level caches need to have higher capacities, but can afford to be slower, so they use smaller transistors that are packed more tightly.