Page "Cache (computing)" Paragraph 5

When the cache client ( a CPU, web browser, operating system ) needs to access a datum presumed to exist in the backing store, it first checks the cache.

If an entry can be found with a tag matching that of the desired datum, the datum in the entry is used instead.

This situation is known as a cache hit.

So, for example, a web browser program might check its local cache on disk to see if it has a local copy of the contents of a web page at a particular URL.

In this example, the URL is the tag, and the contents of the web page is the datum.

The percentage of accesses that result in cache hits is known as the hit rate or hit ratio of the cache.