Motorola 68020


Motorola 68020

(processor)A microprocessor from Motorola. It was thesuccessor to the Motorola 68010 and was followed by theMotorola 68030. The 68020 has 32-bit internal and externaldata and address buses and a 256-byte instruction buffer,arranged as 64 direct-mapped 4-byte entriesThe 68020 added many improvements to the 68010 including a32-bit ALU and external data bus and address bus, andnew instrucitons and addressing modes. The 68020 (and68030) had a proper three-stage pipeline.

The new instructions included some minor improvements andextensions to the supervisor state, some support forhigh-level languages which didn't get used much (and wasremoved 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 indirectionto many of the pre-existing modes, and added quite a bit offlexibility to various indexing modes and operations.

The instruction buffer (an instruction cache) was 256bytes, arranged as 64 direct-mapped 4-byte entries. Althoughsmall, it made a significant difference in the performance ofmany applications.

The 68881 and the faster 68882 FPU chips could be used withthe 68020.

The 68020 was used in many models of the Apple Macintosh IIseries of personal computers and Sun 3 workstations.