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What is L1, L2, and L3 CPU cache? How does it work?

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CPU caches are small memory pools that store information or data that the CPU is most likely to use next. The data loaded into the cache memory is decided by complex algorithms that are embedded into the software.

The main goal of the cache memory is to make sure that the CPU faces minimum time delay or latency while transferring data or when in need of data. When the CPU needs the next bit of data, it will use the data that is stored in cache memory. This is called as a cache hit.

Whereas, a cache miss means the CPU has to go searching for the data it needs elsewhere. This is where the L2 (Level 2) cache comes into play and has a much larger memory size than the L1 (Level 1) cache but is slower. If data can’t be found in the L2 cache, the CPU continues down the chain to L3, and then the main memory (DRAM).

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What are L1, L2, and L3 CPU cache and how they work?

There are three types of CPU cache and work in the following order:

  • (L1) Level 1 Cache (2KB – 64KB): Instructions are first searched in this cache. L1 cache very small in comparison to others, thus making it faster than the rest.
  • (L2) Level 2 Cache (256KB – 512KB): If the instructions are not present in the L1 cache then it looks in the L2 cache, which is a slightly larger pool of cache, thus accompanied by some latency.
  • (L3) Level 3 Cache (1MB -8MB): With each cache miss, it proceeds to the next level cache. This is the largest among the all the cache, even though it is slower, it’s still faster than the RAM.

L1 caches are designed to be the fastest as they are closest to the CPU and thus it will be accessed typically by the CPU and the access time of L1 cache has a major effect on the clock rate of the CPU. L1 caches are normally much smaller than the other levels of cache but are much bigger than the CPU’s registers.

L2 however, is relatively slower but is bigger in size giving higher hit rates. L3 is slower as far as the access time is considered (not as slow as the main memory) and even bigger when the size is considered w.r.t. L2. This continues for all the cache levels.

The basic purpose of cache memory is to store program instructions that are frequently re-referenced by software during operation. Fast access to these instructions increases the overall speed of the software program.

The main function of a cache memory is to speed up the working mechanism of the computer.

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Rajiv Kulkarni

Rajiv Kulkarni