A Cache is a block of memory used for temporary storage of data (ie: webpages, etc..) that is likely to be used again. Your CPU and hard drive frequently use a Cache, as do web browsers and web servers. A Cache is made up of a pool of entries. Each entry has a piece of data or copy of the original information which can be stored in multiple locations. Each entry also has a tag, which specifies the identity of that
particular peice of data in your storage. When the Cache client (web browser, ISP, or operating system) wishes to access this data it first checks the Cache. This helps save time and reduces the workload on the system using the Cached client. If you use your web browser and an entry can be found with a tag matching that of the desired data, then the Cached version is used instead. This situation is known as a Cache Hit. When the Cache is consulted and found not to contain data with the desired tag, it is known as a Cache Miss.
So, for example, a web browser program might check its Local Cache stored on your computer to see if it has a local copy of the contents of a web page at based on a particular URL. In this example, the URL is
the tag, and the contents of the web page is the data. The percentage of accesses that result in Cache Hits or Cache Misses is known as the Hit Rate or Hit Ratio of the cache.
Most systems fetch and retrieve updated versions of your stored data or Cache every 18-72 hours. This means that your ISP and your local system can at anytime have an out of date version of your data (i.e. website) in its Cache. If you have updated your website, migrated servers or changed web hosts you may not immediately see the changes you made. This could be because your local system has an out of date copy or your ISP’s system has not clear their Master Cache. Follow the steps below to clear your local systems Cache first. If this does not do the trick then you may need to contact your ISP and request they manually flush their current cache. Depending on the ISP if they refuse you will have to wait for them to automatically clear their Cache which may take 18-72 hours for them to do.