Motorola 68020
The Motorola 68020 is a 32-bit microprocessor developed by Motorola. Released in 1984, it was a significant advancement in the Motorola 68000 series of processors, which also includes the Motorola 68010 and the Motorola 68000. The 68020 was the first fully 32-bit processor in this series, featuring 32-bit internal and external data and address buses, in contrast to its predecessors that had 16-bit data and 24-bit address buses.
Architecture and Features
The Motorola 68020 was designed with a 32-bit Arithmetic Logic Unit (ALU), allowing it to perform 32-bit operations in a single clock cycle. This was a notable improvement over the Motorola 68000, which required at least two cycles for such operations due to its 16-bit ALU. The 68020's architecture enabled higher processing speeds and improved computational efficiency.
Another enhancement was its ability to handle up to 4 GB of memory address space, a feature facilitated by its 32-bit address bus. This was a substantial increase over previous models, which were limited to addressing 16 MB. The 68020 also introduced support for on-chip instruction and data caches, improving performance by reducing bottlenecks in memory access.
Usage and Applications
The Motorola 68020 was widely used in various computing systems, including some early Apple Macintosh computers like the Macintosh II. It was also incorporated into embedded systems and other computing devices needing robust performance capabilities.
The processor was often paired with the Motorola 68881 or Motorola 68882 floating-point units (FPUs), which were used to enhance the floating-point computational capabilities of systems using the 68020. These FPUs were particularly important for applications requiring extensive mathematical computations, such as scientific and engineering software.
Successors and Variants
The Motorola 68020 was succeeded by the Motorola 68030, which included an on-chip Memory Management Unit (MMU) and other enhancements. The 68030 maintained the 32-bit architecture while providing additional features that improved overall system performance.
A lower-cost version of the 68020, known as the 68EC020, was also produced. This variant was designed for applications that did not require the full capabilities of the original 68020 and was used extensively in embedded systems.