Despite that it has been known for a while, the time has now simply come. PHP 4 has received its final release, version 4.4.9. The last security fix, the last bug fixes, and the last time it will get support. It’s time for PHP 5. If you run a web site at a hosting provider, or perhaps are your own host .. this blog entry is a required read for you.
Bigger PHP applications, such as vBulletin can gain a lot of increased performance from running a PHP op-code cache/accelerator such as APC.
Here are some instructions on how install APC on various systems, my personal experience is with what appears the most common: 32bit CentOS 5 Server.