Z80
The Z80 is an 8-bit little-endian CPU designed by Zilog.
All NeoGeo systems use it to handle sound and music playback. It runs at 4MHz and only has access to the YM2610, M1 ROM or Z80 files, and its own RAM.
Since it doesn't share a RAM area with the 68k CPU like on the Sega Genesis, it can't be used efficiently to perform gameplay-related tasks.
See Z80 memory map and Z80 port map.
Datasheet
Official Z8400 datasheet: [[1]]