One of the easiest and best ways to improve Joomla performance on a high traffic web site is by using Memcached.

Memcached is well supported on most operating systems. On the Windows platform Memcached is commonly installed and run as a Windows Service. There are typically two services running at any given time, one for caching data and another for caching sessions. The Memcached configuration is located in the Windows registry and the amount of memory used by Memcached can be set.

The original Joomla JMemache project can be found here. Starting with Joomla 1.5 the Memcached support was built directly into the core API. Installing Memcached is a fairly straight forward process and it is one of the easiest and least expensive ways to boost Joomla performance.

There are other caching options available for PHP as well includeing eAccelerator and APC.