CPU: NEC 780C @ 3.579545 MHz (3.546893 MHz on PAL)
GFX: Texas Instruments TMS9928A (custom) (TMS9929A on PAL)
SND: Texas Instruments SN76489A (clones)
MEM: 8 kB System / 16 kB Video
RES: 256x192 or 256x224 (256x240 on PAL/SECAM)
The processor is a clone of the Zilog Z80.
There was also an Yamaha YM2413 FM sound chip on early Japanese models.
Released originally as Sega Mark III in Japan in 1985 with a different casing.