One of the Best way to optimize the PHP and Apache Performance is to install a PHP Accelerator and Optimizer on server, They are many Accelerators available in market Below are the Some of the best Accelerators available today. We can install these on products like Magento, WordPress, Drupal, OSCommerce, X-cart, Zen-Cart etc.
But for Magento Only Latest Versions Greater then 1.4 Supports.
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.
Memcached is an in-memory key-value store for small chunks of arbitrary data (strings, objects) from results of database calls, API calls, or page rendering.
Memcached is simple yet powerful. Its simple design promotes quick deployment, ease of development, and solves many problems facing large data caches. Its API is available for most popular languages.
Download link http://code.google.com/p/memcached/downloads/list
eAccelerator is a free open-source PHP accelerator & optimizer. It increases the performance of PHP scripts by caching them in their compiled state, so that the overhead of compiling is almost completely eliminated. It also optimizes scripts to speed up their execution. eAccelerator typically reduces server load and increases the speed of your PHP code by 1-10 times.
eAccelerator stores compiled PHP scripts in shared memory and executes code directly from it. It creates locks only for a short time, while searching for a compiled PHP script in the cache, so one script can be executed simultaneously by several engines. Files that can’t fit in shared memory are cached on disk only.
Download Link http://bart.eaccelerator.net/source/0.9.6.1/
APC Alternative PHP Cache
The Alternative PHP Cache (APC) is a free and open opcode cache for PHP. Its goal is to provide a free, open, and robust framework for caching and optimizing PHP intermediate code.
Installing/Configuring Table of Contents http://www.php.net/manual/en/apc.setup.php
* Runtime Configuration
* Resource Types
Download Link http://pecl.php.net/get/APC-3.0.14.tgz