Output Caching: Output caching is useful when the contents of an entire page can be cached. While a page is cached by the output cache, subsequent requests for that page are served from the output page without executing the code that created it.
Fragment Caching: Sometimes it is not practical to cache an entire page - perhaps portions of the page must be created or customized for each request. In this case, it is often worthwhile to identify objects or data that are expensive to construct and are eligible for caching. Once these items are identified, they can be created once and then cached for some period of time. Additionally, fragment caching can be used to cache regions of a page's output.
Data Caching: Data caching is storing data in memory for quick access. Typically information that is costly to obtain (in terms of performance) is stored in the cache. One of the more common items stored in a cache is commonly displayed database values; by caching such information, rather than relying on repeated database calls, the demand on the Web server and database server's system resources are decreased and the Web application's scalability increased. The cache items can be given an expiration policy that causes them to be removed from the cache when they have expired. Code that accesses the cache item simply checks for the absence of the item and recreates it, if necessary.
