After the CPU receives an instruction, it will first go to the first level cache (L1 Cache) in the CPU to look for the relevant data, but the L1 Cache is running at the same frequency as the CPU, but due to its small capacity, it can't hit every time. At this point, the CPU will continue to look for the next level of L2 cache, and by the same token, when the required data is not available in L2 cache, it will continue to turn to L3 cache (if there is a L3 cache, such as Xeon, Phenom, etc.), memory (main memory), and hard disk.