Complex sentence: The Athlon XP-M replaced the older Mobile Athlon 4 based on the "Palomino" core, with the Athlon XP-M using the newer "Thoroughbred" and "Barton" cores.
Split into simpler sentences: The Athlon XP-M replaced the older Mobile Athlon 4. The Mobile Athlon 4 used the older "Palomino" core, while the Athlon XP-M used the newer "Thoroughbred" and "Barton" cores.