In a new post Sherif Ramadan takes an in-depth look at PHP arrays and what happens behind the scenes when they're put to use.

PHP is one unique language where the array data type has been highly generalized to suit a very broad set of use cases. [...] I’m going to share with you some of the underlying details of how the PHP array data type works, why it works the way that it does, how it’s different from other languages, and what behaviors the PHP array has that you may not be fully aware of.

He starts with a section looking at what arrays actually are in PHP (and how they compare to the lower level C arrays). He gives a C-based array example and shows how it's stored in memory. He points out how PHP arrays are different from other languages and shows the C code that works behind the scenes to create the array (actually a hashtable). He gets into a detailed explanation of the iteration of arrays including some basic benchmarks of some of the various methods and gets more in-depth with foreach (including subarrays and arrays containing references).