3.58MHz (I think) 65816 processor (basically 16-bit version of 6502). ? MB RAM. Custom sound processor with 64kb of onboard RAM. Custom video hardware. (512 resolution, 32k colours - 256 on screen at once - hardware sprites, hardware scaling and rotation)
Also had the ability to have a coprocessor in the cartridge - used to give a 3d upgrade by about three games.