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L1 and L2 Caches

The whole idea is to keep staging more instructions and data in a high-speed memory closer to the CPU.

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An Instruction Cache

This conceptual animation shows how a cache speeds up instruction fetching. Note how fast the instructions are copied from main memory to the L2 cache and then from the L2 cache to the CPU (actually the L1 cache in the CPU). If the faster static RAM (SRAM) were as inexpensive as dynamic RAM (DRAM), there would be no need for an L2 cache.

Disk Caches A disk cache is a section of main memory or memory on the disk controller board that bridges the disk and the CPU. When the disk is read, a larger block of data is copied into the cache than is immediately required. If subsequent reads find the data already stored in the cache, there is no need to retrieve it from the disk, which is slower to access. If the cache is used for writing, data are queued up at high speed and then written to disk during idle machine cycles by the caching program. If the cache is built into the hardware, the disk controller figures out when to do it. See cache coherency, write back cache, write through cache, pipeline burst cache, lookaside cache, inline cache, backside cache and NV cache.

Disk Cache

Disk caches are usually just a part of main memory made up of common dynamic RAM (DRAM) chips, whereas memory caches (CPU caches) use higher-speed static RAM (SRAM) chips.

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