According to http://memcached.org/ It is a Free & open source, high-performance, distributed memory object caching system, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load.
What is memcache and why you use memcache for your website
Installing Memcached on Linux System
I write the command for Installing memcached on ubuntu but it works well for many linux flavors.
To install memcached open terminal write the following command
sudo apt-get install memcached
After installing memcached on your system open the configuration file to set the memory and port number for memcached.
// This is the default setting you can set this according to your requirements
once you set the value then save the file and restart the daemon
sudo /etc/init.d/memcached restart