A disk caching strategy: when an application reads a block from a file, and unless the I/O subsystem has reason to believe that the application is reading the file other than sequentially, a proactive read of the next block is automatically scheduled, meaning that when the application asks for it, it'll probably be in the cache already.

If you have an I/O cache at all, readahead is easy to implement, and gives you good bang for the buck.