68000 series

68000 series. The 68000 series is a family of 16/32-bit CISC microprocessors developed by Motorola beginning in the late 1970s. It became widely renowned for its clean, orthogonal architecture and was a primary competitor to Intel's x86 architecture throughout the 1980s and early 1990s. The architecture found success in a diverse range of systems, from personal computers and workstations to video game consoles and embedded controllers.

History and development

The project was initiated by Motorola in 1976, led by Tom Gunter, as a successor to the popular Motorola 6800 8-bit microprocessor. The design team, which included engineers like John Buchanan, sought to create a powerful, easy-to-program architecture suitable for future Unix-based systems and advanced applications. The first chip, the MC68000, was introduced in 1979, with key manufacturing partnerships established with Rockwell International and Signetics. Its development was contemporaneous with other seminal 16-bit designs like the Intel 8086 and the Zilog Z8000. The architecture was later extended with the fully 32-bit MC68020 in 1984, cementing its role in technical workstations from companies like Sun Microsystems and Silicon Graphics.

Architecture and features

The architecture is built around a highly orthogonal instruction set and a large linear address space, eschewing the segmented memory model of its contemporary rival, the Intel 80286. It features sixteen 32-bit general-purpose data and address registers, a separate 32-bit program counter, and a status register. The processor uses a Harvard architecture-inspired internal implementation but presents a pure von Neumann architecture model to the programmer. Key features included from the outset were a powerful exception handling system for interrupts and traps, and support for both user mode and supervisor mode operation, which facilitated robust multitasking operating systems like Unix System V and AmigaOS.

Variants and derivatives

The initial MC68000 was followed by the cost-reduced MC68008 with an 8-bit data bus. The fully 32-bit internal and external MC68020 introduced an on-chip instruction cache and enhanced addressing modes. The MC68030 integrated a memory management unit (MMU) and data cache on-die. The MC68040 was a highly integrated design with pipelined execution units and separate FPUs. For embedded control, the family evolved into the CPU32 core, used in microcontrollers like the MC68332. Later, Motorola spun off the architecture into the fully static, lower-power 68EC000 and 68HC000 variants. The architectural lineage ultimately continued in the separate ColdFire and PowerPC product lines.

Applications and market impact

The processor family achieved legendary status as the heart of several iconic personal computers, including the Apple Macintosh, Commodore Amiga, and Atari ST. It powered a generation of technical workstations from Apollo Computer, Sun Microsystems, and NeXT. In entertainment, it was the central processor for seminal video game consoles like the Sega Genesis and arcade boards from Capcom and SNK. Its clean design made it a favorite in academia for teaching computer architecture and a staple in embedded systems for printers, industrial controllers, and telecommunications equipment from Northern Telecom. The architecture's influence waned in the 1990s with the rise of RISC processors like the SPARC and MIPS, and the increasing dominance of the Wintel platform.

Technical specifications

The original MC68000 was fabricated using HMOS technology, contained approximately 68,000 transistors, and typically ran at clock speeds of 8, 10, or 12.5 MHz. It presented a 16-bit external data bus and 24-bit address bus, enabling access to 16 MB of physical memory. Later members of the family scaled significantly; the MC68040, built on CMOS technology, contained about 1.2 million transistors and operated at speeds up to 40 MHz. The instruction set supported a wide range of data types and operations, including binary-coded decimal (BCD) arithmetic. Family members maintained a high degree of software compatibility, with object code compatibility from the MC68000 through the MC68030.

Category:Microprocessors Category:Motorola microprocessors Category:Computer-related introductions in 1979