The robots are controlled by an 8-bit Hitachi processor embedded in an oversized Lego brick called the RCX.

FORBES: Odd creatures

Completed programs are downloaded to the RCX via the infrared port and the robots have a limited ability to communicate with each other.

FORBES: Odd creatures

Singing Lego Blocks: The Lego Mindstorms RCX block (the brain of the system) has a built in speaker, and this page explains in eye-watering detail how to make music with it.

ENGADGET: Music Thing: Musical instruments made of Lego