<
processor> A
microprocessor from
Motorola. It was the successor to the
Motorola 68010 and was followed by the
Motorola 68030. The 68020 has 32-bit internal and external data and address buses and a 256-byte
instruction buffer, arranged as 64
direct-mapped 4-byte entries[?].
The 68020 added many improvements to the 68010 including a 32-bit
ALU and external
data bus and
address bus, and new instrucitons and
addressing modes. The 68020 (and 68030) had a proper three-stage
pipeline.
The new instructions included some minor improvements and extensions to the supervisor state, some support for
high-level languages which didn't get used much (and was removed from future 680x0 processors[?]), bigger (32 x 32-bit) multiply and divide instructions, and bit field manipulations.
The new adderessing modes added another level of indirection to many of the pre-existing modes, and added quite a bit of flexibility to various indexing modes and operations.
The
instruction buffer (an
instruction cache) was 256 bytes, arranged as 64 direct-mapped 4-byte entries. Although small, it made a significant difference in the performance of many applications.
The 68881 and the faster 68882
FPU chips could be used with the 68020.
The 68020 was used in many models of the
Apple Macintosh II series of
personal computers and
Sun 3
workstations.
(2001-03-07)
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