Motorola 68020

Motorola 68020. The Motorola 68020 is a 32-bit microprocessor introduced by Motorola in 1984. It represented a major advancement over its predecessor, the Motorola 68010, by featuring a full 32-bit ALU and data bus. The chip's enhanced performance and new features made it a cornerstone in many high-end workstation and minicomputer designs throughout the mid-to-late 1980s.

History and development

The development of the Motorola 68020 was driven by the need for greater performance in the competitive microprocessor market of the early 1980s. Engineers at Motorola sought to create a true 32-bit successor to the popular Motorola 68000 family. Key figures in its design included Tom Gunter and other architects at the company's Austin, Texas facility. Its announcement and sampling in 1984 positioned it directly against contemporary processors like the Intel 80386. The launch was a significant event for the industry, covered extensively in publications like BYTE (magazine) and Electronics (magazine).

Architecture and features

The architecture of the Motorola 68020 featured several groundbreaking improvements. It implemented a three-stage instruction pipeline and an on-chip instruction cache to boost execution speed. New addressing modes included scaled indexing and larger displacement ranges, enhancing the efficiency of compiler-generated code. The processor also introduced coprocessor interface support, allowing for the direct attachment of units like the Motorola 68881 floating-point unit. This Harvard architecture-inspired cache design and the fully 32-bit internal implementation marked a clear departure from earlier members of the Motorola 68000 family.

Technical specifications

The Motorola 68020 was fabricated using HMOS technology, initially with a feature size of 2.0 µm. It contained approximately 200,000 transistors on a die measuring around 101 mm². The processor operated at clock speeds ranging from 12.5 MHz to 33 MHz. It featured a 256-byte instruction cache and supported a physical address bus of 32 bits, enabling direct access to 4 GB of memory. Unlike the Motorola 68000, it lacked an asynchronous bus, utilizing a synchronous bus protocol that required clock signal alignment for all transfers.

Variants and derivatives

Several variants of the Motorola 68020 were produced to address different market needs. The Motorola 68EC020 was an embedded controller version with a 24-bit external address bus. The Motorola 68020 was also produced in lower-power CMOS versions, such as the 68HC000, for portable applications. A notable derivative was the Motorola 68030, which integrated the MMU and a data cache on-chip. The core architecture also influenced later processors in the family, including the Motorola 68040 and the Motorola 68060. Licensed versions were produced by other companies, including Hitachi and Signetics.

Applications and impact

The Motorola 68020 found widespread use in high-performance computer systems during the 1980s. It was the central processor in the Apple Macintosh II and the Sun Microsystems Sun-3 workstation series. Other notable implementations included the Hewlett-Packard HP 9000 Series 300, the Commodore Amiga 2500/30, and the NeXT Computer board. Its power made it a favorite for UNIX systems and technical applications, influencing the design of later RISC processors from companies like MIPS Technologies and Sun Microsystems. The processor's legacy is evident in its long lifespan in embedded systems and its role in cementing the Motorola 68000 series as a dominant architecture in professional computing. Category:Motorola microprocessors Category:32-bit microprocessors Category:1984 introductions