Memcached is a server side caching system. It is a high-performance, distributed memory object caching system. Its primary purpose is to speed up database-driven websites and applications.
A caching system can dramatically improve the performance of your website. Users of Memcached include WordPress, Wikipedia, Twitter, Youtube, and Flickr, among others.
How does Memcached work?
Memcached stores data and objects in RAM (memory) to reduce the number of times an external data source (such as a database or API) must be read. It has the ability to store SQL queries, that way the next time the query is run, it can return the result from memory.
Difference between Memcached and other caching systems
Other systems allow you direct access to the cached information. Memcached caches data and not parsed scripts. This makes Memcached perfect to optimize MySQL. It is better suited for use with large caches that change.
What is Memcache?
Memcache is the PHP extension for Memcached. The two must be used together to function properly. Just having Memcached on the server will not improve your site's performance. You must modify your coding to use it correctly.