If the information is not in cache, it still has to be retrieved from main memory, but checking cache memory takes so little time, it's worth it. Cache memory makes sense because there's a good chance that the data and instructions the CPU is using now will be needed again. When cache is full and the CPU calls for a new instruction, the system overwrites the data in cache that hasn't been used for the longest period of time. This way, the high priority information that's used continuously stays in cache, while the less frequently used information drops out. Cache , the next level of cache is numbered L2, then L3, and so on.
Computers often have other types of caching in addition to cache memory.
For example, sometimes the system uses main memory as a cache for the hard drive. While we won't discuss these scenarios here, it's important to note that the term cache can refer specifically to memory and to other storage technologies as well. Also, while cache memory does improve overall system performance, it does so up to a point. The real benefit of cache memory is in storing the most frequently-used instructions. A larger cache would hold more data, but if that data isn't needed frequently, there's little benefit to having it near the processor.