68020

68020
David Monniaux · CC BY-SA 3.0 · source
Name	68020
Produced	Motorola
Launched	1984
Architecture	32‑bit CISC
Predecessor	68010
Successor	68030

68020

Introduction

The 68020 was a 32‑bit microprocessor introduced by Motorola in 1984, succeeding Motorola 68010 and preceding Motorola 68030 in the Motorola 68000 series. It was used in systems from Apple Inc. to Commodore, and influenced designs in Sun Microsystems workstations and Cray Research I/O controllers. Development involved collaboration among engineers with experience from Fairchild Semiconductor and Texas Instruments, and its release affected markets alongside processors such as the Intel 80386, Zilog Z8000, and National Semiconductor NS32000.

Architecture

The chip implemented a fully 32‑bit data and address path like contemporary designs from Intel and AMD and featured a separate ALU and shifter similar in concept to units in Motorola 68000 series derivatives. Microarchitecture improvements drew on concepts explored at Bell Labs and in research by teams associated with Stanford University and Massachusetts Institute of Technology. The 68020 incorporated a three‑stage pipeline and supported background exception handling influenced by designs in DEC VAX implementations. Its bus interface was compatible with systems using controllers from National Semiconductor and board designs akin to those in Sun-2 and Amiga platforms.

Instruction Set and Enhancements

The instruction set extended earlier encodings found in predecessors and added capabilities used by compilers from vendors like GCC and Watcom. New addressing modes and instructions paralleled features in architectures such as the SPARC and MIPS families, while preserving compatibility with code written for Motorola 68000. Enhancements included full 32‑bit arithmetic, improved shift and rotate operations similar to those in DEC Alpha whitepapers, and support for a more orthogonal set of opcodes known to compiler writers at Bell Labs and University of California, Berkeley. The processor also provided coprocessor interfacing conventions that were later used by floating‑point units developed by Weitek and Motorola FPU teams.

Performance and Benchmarks

Initial benchmarks compared the chip to Intel 80286 and early Intel 80386 samples, showing competitive integer throughput in tasks used by SPEC and academic suites at Carnegie Mellon University. Performance in graphics and desktop publishing workloads was evaluated on machines from Apple Computer and Commodore International, while workstation performance metrics came from platforms by Sun Microsystems and Silicon Graphics. Memory‑bound tests used DRAM subsystems supplied by Hitachi and Micron Technology, and I/O stress tests were run with controllers from Adaptec and Western Digital.

Implementations and Use in Systems

Manufacturers integrated the processor into diverse product lines: personal computers by Apple Inc. (in expansion cards), systems by Commodore International, and professional workstations by Sun Microsystems and Apollo Computer. Embedded applications appeared in networking gear from Cisco Systems and industrial controllers by Siemens and Fujitsu. The chip was used in peripherals designed by National Semiconductor partners and in academic projects at MIT and Caltech. It also surfaced in products competing against platforms based on Intel and Motorola 68030 designs.

Compatibility and Upgrades

Backward compatibility with software for earlier series members allowed operating systems such as Unix System V derivatives, BSD, and proprietary kernels from Apple Inc. to be ported with fewer modifications. Upgrade paths often involved replacing earlier 68000 or 68010 CPUs or adding accelerator cards by vendors like Phase5 and Ametek. Hardware interfaces followed bus conventions used in VMEbus and expansion standards employed by Amiga third‑party markets, enabling integration with existing chassis and peripherals by manufacturers including TEAC and ATA interface designers.

Variants and Packaging

Motorola offered the processor in multiple speed grades and packaging options to meet platforms from PCB vendors such as Fujitsu and NEC. Packaging formats matched socket types common in systems produced by Apple Computer and workstation vendors like Silicon Graphics. Third‑party firms produced derivative boards and accelerator modules for hobbyist markets centered around Commodore Amiga and clone producers, and custom ASIC implementations appeared in designs by companies partnering with Motorola Semiconductor.

Category:Microprocessors