The Motorola 68000 Microprocessor

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.

Several other companies were second-source manufacturers of the HMOS 68000. These included:

• Hitachi (HD68000), who shrank the feature size to 2.7 µm for their 12.5 MHz version,
• Mostek (MK68000),
• Rockwell (R68000),
• Signetics (SCN68000),
• Thomson/SGS-Thomson (originally EF68000 and later TS68000),
• Toshiba (TMP68000).

Toshiba was also a second-source maker of the CMOS 68HC000 (TMP68HC000).