What is meant by cache hit and cache miss?

A cache hit occurs when requested data is found in a cache, while a cache miss is when it isn't found.

In more detail, a cache is a hardware or software component that stores data so future requests for that data can be served faster. When a computer needs to access data, it first checks the cache. If the data is there, this is known as a cache hit. The computer can then quickly retrieve the data from the cache, rather than having to retrieve it from the main memory, which is a slower process.

On the other hand, if the data is not in the cache, this is known as a cache miss. The computer then has to retrieve the data from the main memory or another location, which takes longer. After a cache miss, the data is usually added to the cache so it will be quicker to access next time.

The ratio of cache hits to cache misses is a key performance indicator for a cache. A high cache hit rate means that the cache is working effectively, speeding up data access and improving the performance of the computer. If the cache miss rate is high, it may be that the cache is too small or not well organised, and the computer's performance may be slower as a result.

Caches are used in various parts of a computer system, including the CPU, web browsers and databases. They are a crucial part of how computers work, and understanding cache hits and misses is important for anyone studying computer science.