Motorola MC68000
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| MC68000 | |
 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.
External links
- 68000 - documentation at Bitsavers
- MC68000 16-Bit Microprocessor - data sheet
