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| 68000 | |
|---|---|
| Name | Motorola 68000 |
| Caption | Early microprocessor in DIP package |
| Produced | 1979–1990s |
| Designer | Motorola Semiconductor Products Sector |
| Bits | 16/32-bit |
| Design | CISC |
| Successor | Motorola 68010 |
68000
The Motorola 68000 microprocessor family is a line of CISC microprocessors introduced in 1979 and used widely in personal computers, workstations, arcade machines, and embedded systems. It combined a 16-bit external data bus with a 32-bit internal architecture that influenced designs across Apple Inc., Atari Corporation, Commodore International, Sun Microsystems, and Sega Corporation. Its balance of orthogonal instruction encoding, addressing modes, and register organization made it popular in both commercial and hobbyist communities such as users of the Amiga, Macintosh, Atari ST, and SEGA Genesis platforms.
Introduced by Motorola as part of a family that included follow-on models used in NeXT Computer, IBM PC/AT-era compatibles, and military systems, the chip targeted minicomputer performance in a single-chip form factor. It featured an architecture that borrowed concepts from PDP-11 and influenced successors at Intel, ARM Holdings, and Sun Microsystems. Designers aimed to support operating systems like UNIX System V, CP/M, and later bespoke kernels for workstation environments developed by companies such as Acorn Computers and Digital Equipment Corporation.
The processor combined a 16-bit external data bus and 24-bit address bus in its original incarnation, enabling 16 MB of addressable memory—used by systems like the Apple Lisa and early Macintosh models. Internally, it used 32-bit registers and arithmetic logic units similar in concept to designs from DEC minicomputers and influenced by the register models seen in VAX architectures. Its register file included eight data registers and eight address registers, an exception model with supervisor and user modes that aligned with protection features required by SunOS and AIX-style operating systems. Interrupt handling and trap vectors were compatible with system designs from Xerox PARC-inspired workstation projects and real-time operating systems used by NASA and Bell Labs research groups.
The instruction set provided a rich set of addressing modes—immediate, absolute, register indirect, indexed, and PC-relative—mirroring flexibility present in PDP-11 heritage designs and easing compiler support for languages like C, Pascal, and FORTRAN. Orthogonal instructions allowed operations between registers, memory, and immediate values, simplifying code generation for compilers used by GCC, Watcom, and vendor toolchains from Borland and Microsoft. Exception vectors and supervisor calls enabled the implementation of multitasking kernels such as those developed by Apple Computer for early Macintosh and by Commodore for AmigaOS. The processor supported binary-coded decimal and bit-field operations that were useful in financial and telecommunications systems built by companies like Siemens and AT&T.
Motorola produced several revisions and derivatives, including models with pipelining, improved bus control, and expanded addressing such as 32-bit address variants used in high-end workstations from Sun Microsystems and NeXT. Third-party vendors created licensed versions and clone implementations for embedded markets served by Philips, Texas Instruments, and Fujitsu. The family spawned low-power and high-performance versions for use in arcade hardware by Capcom and Konami, console adaptations for Sega, and hardened variants for aerospace and defense contractors such as Raytheon and Lockheed Martin.
Early clock rates compared favorably to contemporary microprocessors from Intel and Zilog, offering strong single-threaded performance for desktop applications like word processing on Macintosh systems and graphics workloads on Amiga machines. The architecture was favored by developers of computer-aided design systems at Silicon Graphics and workstation-class software at Sun Microsystems because of its 32-bit internal registers and predictable instruction timings that benefited compilers from HP and IBM. In arcade and console markets, its use in systems by Sega and Atari powered titles from developers such as Capcom USA and Taito while embedded versions controlled industrial equipment from Siemens and telecommunications switches from Nortel Networks.
The processor's orthogonal instruction set, register model, and ease of compiler generation influenced later RISC and CISC designs at ARM Holdings, Intel Corporation's architecture teams, and research projects at University of California, Berkeley and Stanford University. It left a lasting imprint on software ecosystems including operating systems like AmigaOS, Mac OS Classic, and early UNIX ports, and on gaming history through systems from Sega and Atari Corporation. Enthusiast and preservation communities around retrocomputing and museums such as the Computer History Museum continue to maintain collections and documentation for systems built around this family.
Category:Microprocessors Category:Motorola products