(9) How does L3 or L4 cache memory work in a PC? - Quora

(9) How does L3 or L4 cache memory work in a PC? - Quora

I think 'Do we need a L3 or L4 cache?' is a better question to start with. By the way you asked this question, I presume that you already know why we use L1 and L2 cache memories.
Let's try to understand this with a simple analogy.
Assume that a social welfare society is trying to pack food for starving children into packets. Each packet consists of some of rice.
Now, there is a huge reserve of rice that is 10 minutes of walk from the place you are packing. It is easy to imagine how inefficient it is to bring rice every time you are trying to pack a single bag. So, a better way to solve this problem is to keep a smaller reserve of rice at your table and assign a person to fill your sub reserve from the main rice reserve, whenever you are going to run out of rice. But let's assume that your packing speed is too fast, that you are emptying the reserve with in 10 minutes. Now, you might need 2 people to bring rice instead of one, to fill your reserve for every 5 minutes. But, now if we have a packing super hero 'PACKMAN :P' trying to empty the reserve for every 2 minutes, you will be needing a third person to cover the latency.
Here, the caches play the role of your helpers and the PACKMAN is the processor. It is totally a design decision to choose the number of helpers you need to keep the PACKMAN from being idle. The faster your processor executes, the more important is the need to increase levels/efficiency of caching.
However, there is another side to this story. As you keep increasing the levels of cache, the hit rate on last levels of cache get skewed by initial levels of cache. Therefore it becomes pointless to have numerous cache levels. The decision has to be made keeping the processor workload in mind. If you are planning to design the processor for workloads which involve random memory requests, then multi level caching will not help. See this paper for reference to effect of workloads on cache performance,

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