“The advantage of embedded Linux is that it’s a royalty-free, open source, compact solution that provides a strong foundation for an ever-growing base of applications to run on. Linux is a fully functional operating system, with support for a variety of file-handling protocols, network protocols, devices – a very important requirement in embedded systems because of the need to ‘compute anywhere, anytime’. It is modular in nature and is easy to slim down by removing utility programs, tools, and other system services that are not needed in an embedded environment.”
This linux version is the one which runs on an ipod.
http://ipodlinux.org/Main_Page