For those interested in understanding how chess programs work, also see Toledo Nanochess: The commented source code

http://www.lulu.com/shop/oscar-toledo-gutierrez/toledo-nanoc...

  Toledo Nanochess is the world's current smallest chess 
  program written in C language. Now for the first time is 
  published the complete documented source code. Also 
  including the documented source code of the JS1K 2010 
  Chess entry (2nd place winner)