Motorola MC68000

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MC68000 in a Macintosh SE
Family: Motorola M68000 Family
Architecture: 32-bit
Manufacturer: Motorola
Year Introduced: 1979
Address bus: 23-bit (16-bit word address)
Data bus: 16-bit
Number of registers: 15 general 32-bit registers (8 data, 7 address)
Clock Speed: 4 MHz - 16.67 MHz

The Motorola MC68000 was the first member of the Motorola M68000 Family of VLSI microprocessors. Although it was described by Motorola as a "16-bit microprocessor", it is generally considered to be a 32-bit architecture; it is probably more correct to describe it as a 16-bit implementation of a 32-bit architecture.

A major failing of the MC68000 was that it could not support virtual memory; not enough internal state was saved when a page fault occurred. Several computer makers worked around this by including two separate MC68000 chips; when a fault occurred, the first CPU was 'frozen', and a second fixed up the fault, then re-started the 'main' CPU. This issue was fixed with the successor chip, the MC68010.

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