Preload is an adaptive read-ahead daemon. It monitors applications that users run, and by analyzing this data, predicts what applications users might run, and fetches those binaries and their dependencies into memory for faster startup times.
It runs as a daemon in the background so it is unobtrusive to your desktop. To install Preload open up Terminal and type in;
sudo apt-get install preload
For example, if you run Firefox, GAIM, and OpenOffice everyday Preload will determine these are common applications and will keep the libraries in your RAM before you even load them up – this leads to a faster startup time. Preload is also adaptive enough to determine if you change your working habits as well.
Preload does not need to be configured, it is adaptive and merely relies on a count of the number of times an application is launched to perform the preload.
Do not confuse Preload with Prefetch which is still under development and is expected to be part of Gutsy Gibbon in October 2007.
Nor is it to be confused with squid-prefetch which preloads web-pages.
The source article here