On PHPMaster.com there's a new tutorial from Timothy Boronczyk focusing on the binary operators in PHP and using them to do some base conversions.
This article discusses PHP’s binary operators and how to convert between different counting systems. Most programming books and articles only dedicate a page or two to such topics, and although using the operators is really quite simple, there’s a fair amount of background knowledge one must have to use them correctly. Instead of giving the same bare-bones treatment that every other reference gives, I’ll first provide you the necessary background in number theory. Armed with that knowledge, you’ll be able to understand the binary counting system and base conversions… and familiarity with binary digits is the key to successful use of the binary operators!
As promised he starts off with some number theory complete with illustrations about base-10 and how the values fit into "buckets" of data. He compares this to base-2 (binary) and only then starts getting into the conversion functions. He shows the usage of things like decbin and dechex to modify the values as well as the use of bitwise and binary operators.