what is the difference between l1 cache and l2 cache?

问题:

I know that l1 and l2 caches are levels in multi-level cache.
I would like to know where each level cache is placed, and what is the maximum number of cache levels allowed?

回答1:

Both of these depend on the CPU. There are CPUs which have no cache at all, there are CPUs which have the L1 cache on die and the L2 cache on a separate die on the same chip or even on a separate chip, or there are CPUs which have both L1 and L2 cache on the same die as the CPU core.

There are multi-core, multi-chip CPUs where each core has its own L1 cache on die, the 4 cores of one multi-core chip share an L2 cache that is on chip, but on a separate die, and the 2 chips share an L3 cache that is on a separate chip, but in the same package. Sometimes, there are also so-called CPU books which contain multiple chip packages, which might or might not have their own shared cache, which would then be an L4 cache.

Of course, multi-core chips don't have to share their L2 cache, they can also have private L2 caches.

And it's not always obvious, what level a certain cache is, or even whether or not a piece of RAM is a cache at all.

For example, on later Intel 80486 processors, there was an L1 cache on the chip and an L2 cache on the motherboard. But then AMD came out with a socket-compatible CPU that had both an L1 and L2 cache on the chip. So, the exact same cache chip on the motherboard was either an L2 or L3 cache, depending on what kind of CPU you used.

not view this as RAM, but more as a software-controlled cache.

回答2:

Taken from this link -

L1 and L2 are levels of cache memory in a computer. If the computer processor can find the data it needs for its next operation in cache memory, it will save time compared to having to get it from random access memory. L1 is "level-1" cache memory, usually built onto the microprocessor chip itself. For example, the Intel MMX microprocessor comes with 32 thousand bytes of L1.

L2 (that is, level-2) cache memory is on a separate chip (possibly on an expansion card) that can be accessed more quickly than the larger "main" memory. A popular L2 cache memory size is 1,024 kilobytes (one megabyte).

Complete Cache architecture is here in WIKI

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