from
The Free On-line Dictionary of Computing (8 July 2008)
Motorola 68020
68020
MC68020
<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)