68000 vs. 68020

Attribute	68000	68020
Architecture	16-bit	32-bit
Instruction Set	CISC	RISC
Performance	7.5 MIPS	17 MIPS
Addressing Modes	7	13
Registers	8 data, 8 address	8 data, 8 address, 8 address control

Introduction

The 68000 and 68020 are both microprocessors developed by Motorola in the 1980s. These processors were widely used in various applications, including personal computers, workstations, and embedded systems. While both processors belong to the same family, they have distinct differences in terms of performance, features, and architecture.

Performance

The 68000 processor, also known as the MC68000, was introduced in 1979 and was the first member of the 68k family. It had a 32-bit data bus and a 24-bit address bus, allowing it to address up to 16 MB of memory. The 68000 had a clock speed ranging from 8 to 12.5 MHz, depending on the version. In contrast, the 68020 processor, introduced in 1984, had a 32-bit data bus and a 32-bit address bus, enabling it to access up to 4 GB of memory. The 68020 had a clock speed of up to 33 MHz, significantly faster than the 68000.

Features

One of the key features of the 68020 processor was its support for virtual memory, which allowed for more efficient memory management and multitasking capabilities. The 68020 also introduced a new instruction set architecture, including new addressing modes and additional instructions, improving overall performance. In comparison, the 68000 lacked support for virtual memory and had a simpler instruction set, limiting its capabilities in multitasking environments.

Architecture

Both the 68000 and 68020 processors were based on a CISC (Complex Instruction Set Computer) architecture, which included a large number of instructions for various operations. However, the 68020 introduced some RISC (Reduced Instruction Set Computer) features, such as a pipeline architecture and improved branch prediction, making it more efficient in executing instructions. The 68000, on the other hand, had a more traditional CISC architecture with a simpler pipeline design.

Compatibility

One of the advantages of the 68020 processor was its backward compatibility with software written for the 68000. This meant that existing applications could run on the newer processor without modification, making it easier for developers to upgrade their systems. However, the 68020 also introduced new features and instructions that were not available on the 68000, requiring software optimizations to take full advantage of the improved performance.

Conclusion

In conclusion, the 68000 and 68020 processors were both significant advancements in the field of microprocessors, offering improved performance and features compared to their predecessors. While the 68000 was a pioneering processor with a simpler architecture, the 68020 introduced new capabilities such as virtual memory support and a more efficient instruction set. Ultimately, the choice between the two processors would depend on the specific requirements of the application and the desired level of performance.