<
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)