Motorola M68000 Family

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The Motorola 68000 family (also 680x0, 68K, etc) is a series of VLSI microprocessors, successor to Motorola's prior Motorola M6800.

Although the first in the series (the MC68000) was described by Motorola as a "16-bit microprocessor", the family is generally considered to be a 32-bit. In a number of important aspects of an architecture:

  • Word (address space) size
  • Register length
  • Many operations (arithmetical, logical, etc)

all shared by all members of the family (which are generally compatible at the object code level) it is a 32-bit machine. (A large share of the instructions are only 16 bits long, however.)

The earliest member of the family (the MC68000) did not support virtual memory or virtualization, but all the later members did. The 68K family is a CISC architecture.

The architecture shows clear influences from the PDP-11 architecture, including auto-increment and -decrement modes for stack support and array operations, memory-mapped I/O, etc. In other ways it has similar approaches to the PDP-11, including large numbers of general-purpose registers, a very orthogonal instruction set, etc, although it is harder to say definitively what the source was.

During their lifetime (in the 1980s and early 1990s), they were popular, initially in small time-sharing systems, and then workstations (e.g. the Sun workstation) and finally in personal computers (notably the Apple Macintosh).

In the latter role, their primary competition was the Intel x86 microprocessor line. They are no longer used in personal computers, but derivatives are still in wide use in embedded systems.

Motorola ceased development of the 68000 family in 1994, when they moved to the Motorola 88000 family of RISC processsors, and soon thereafter the PowerPC family, in collaboration with IBM and Apple Computer.

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