Motorola 68000

The Motorola 68000 (sometimes shortened to Motorola 68k or m68k and usually pronounced "sixty-eight-thousand") is a 16/32-bit complex instruction set computer (CISC) microprocessor, introduced in 1979 by Motorola Semiconductor Products Sector.

The design implements a 32-bit instruction set, with 32-bit registers and a 16-bit internal data bus. The address bus is 24 bits and does not use memory segmentation, which made it easier to program for. Internally, it uses a 16-bit data arithmetic logic unit (ALU) and two more 16-bit ALUs used mostly for addresses, and has a 16-bit external data bus. For this reason, Motorola termed it a 16/32-bit processor.

As one of the first widely available processors with a 32-bit instruction set, large unsegmented address space, and relatively high speed for the era, the 68k was a popular design through the 1980s. It was widely used in a new generation of personal computers with graphical user interfaces, including the Macintosh 128K, Commodore Amiga, Atari ST, and Sharp X68000. The 1988 Sega Genesis/Mega Drive console is powered by a 68000.

Later processors in the Motorola 68000 series, beginning with the Motorola 68020, use full 32-bit ALUs and have full 32-bit address and data buses, speeding up 32-bit operations and allowing full 32-bit addressing rather than the 24-bit addressing of the 68000 and Motorola 68010 or the 31-bit addressing of the Motorola 68012. The original 68k is generally software forward-compatible with the rest of the line despite being limited to a 16-bit wide external bus.

After 45 years in production, the 68000 architecture is still in use.