memcached is a distributed database based upon the principle of a hash table: Ask if an arbitrary key exists, and if it does you get the matching value stored in the hash table. If it doesn't, it will be. Least recently used objects get purged from the table to reclaim memory. memcached instances connect to one another so the hash table can span arbitrary numbers of nodes on a network but be queried with a single line of code. Note that securing your memcached grid is your job: It's designed to be run on a trusted network (i.e., your production network that you've hardened behind a firewall that you manage...)