Intro
Early computers were based on mostly 8 bit processors like the 6502 and 8088 processors. These include the original IBM PC, Apple I/II and Commodore 64 computers as well as many more. These computers thrived between the late 1970’s and well into the 1980’s. But with the release of the Motorola 68000 (or 68k) we saw several new computers hit the market. These systems offered significant power over their predecessors, in clock speed, memory bandwidth, and processor efficiency. The 68k process at launch was unique in its capabilities. Later the Intel X86 would be its most direct peer. But the 68k was unique because it was a clean sheet design. It was not backwards compatible with any existing systems or processors. It did provide some compatibility with peripheral chips designed for earlier processors. But that would only benefit the designers of a computer based on this processor, it provided no benefit to the user of a system based on this processor. So the 68k’s clean sheet design offered great power with a fairly simple design. This design encouraged several companies of the time to abandon previous software and move to this new processor. These included Apple, Atari and Commodore.
What made the 68k processors most unique was that they were really designed from day one as a stepping stone to the next generation of 32-bit processors. Its instruction set and internal design supported 32 bit registers for data and addressing from day one. What made this a 16 bit processor was the fact that the data bus has 16 bits. In fact the address bus for this processor has 23 bits. This allows the 68k to support addressing up to 16 MB of address space. Unlike the Intel processors there was not a separation between IO space and RAM/ROM, so this 16MB address space also included ROM, RAM and “memory mapped” IO registers as well.
[Include memory maps of Atari and Mac]
The 68k processors really drove almost every computer that wasn’t an IBM PC. These include: Apple Macintosh/Lisa, Atari ST, Commodore Amiga, as well as Early systems from Sun microsystem and Silicon Graphics. Part of the reason so many people leverage this architecture was the future looking design. Following the 68000 was the 68010, 68020, 68030, 68040 and finally the 68060. The first processor was released in 1979 and the last was released in 1994, so this architecture provided 15 years of “state of the art” processor design. If you’re familiar at all with these processors you’re probably familiar with the original 68k, the ‘020, ‘030 and ‘040, but you’ve probably not heard of the 68010 or the 68060.
68010
The 68010 was a small step ahead of the original 68k, it was pin compatible with its predecessor, meaning most platforms could simply replace the 68k with the 68010, but it did have a few new instructions and capabilities that meant ROMs would need to be updated for it to be supported. Many manufacturers saw little to know reason to update their designs with this processor since it was a relatively small iteration. It also came out at the same time that many of these companies’ first generation products were launching. So I think they were more focused on improving their OS and software than upgrading HW. Remember Apple would have had the biggest budget, but the Macintosh was initially looking like a failure. Sales were low due to its high price. So much so that Apple II was getting more engineering focus than the Mac. Another observation I have for the 68010 is it feels like it was the processor that Motorola intended the 68000 to be. I wonder if schedule delays caused them to put out an early version of the target product to get the time to market they were looking for? And then the 68010 became that target product when they finished it.
020/030/040
With these processors Motorola officially moved into the 32 bit era. With full 32 bit address and data busses, these processors also offered increased clock speed as well as other operation improvements. The 020 introduced caching to the chip, this would be further expanded on the following generations of chips. The 030 included an integrated memory management unit. This offered systems to implement paged memory systems, this greatly improved the memory management for operating systems and applications. The 040 integrated a floating point processor into the chip as well. This has been available since the original 68k as a separate chip.
This evolution of products and features is closely tied to Intel’s product line. With 286 and 020, 386 and 030 and 486 and 040. With each generation Motorola and Intel matched feature sets and performance. While wikipedia shows that Intel launched these processors about 2 year before Motorola on each generation, computers based on these seemed to hit the market closer to the same time. IBM’s first PC with the 286 was released in 1986 despite the processor officially launching in 1982. Apple released the Mac II in March of 1987 with the 020. Apple would release the Mac IIx with the 030 in 1988. Compaq would release the first 386 based PC in 1986, the same year that IBM launched the 286. And while the hardware was released in PC before the Mac line it was often the case that the Software available at the time on PC didn’t take advantage of the HW, due in part to the software compatibility maintained to the 8 bit days.
[Include chart showing timeline of systems]
68060 End of the Line
By 1994 when the 060 was released just one year before Intel launched the original Pentium (P5) processor. But what killed the 68k line was not the Intel processors, but Motorola’s own Power PC. With the 68k line Motorola was getting beat to the punch at each generation by Intel. Everyone in the 68k world was looking for something that could leap frog Intel. By the 1990, RISC was all the rage in CPU design circles. So Motorola teamed up with, ironically, IBM to create a truly next generation processor called the PowerPC. It leveraged work that IBM had done on the “Power Architecture”, a RISC based 32-bit processor. The PowerPC was designed from day one to support the future of a 64-bit world. The first version of the Power PC, the 601, was released in October of 1992, 2 years before the 060 was released. Motorola diverted a lot of engineering resources to work on the PowerPC. So the 68060 design suffered as a result. Both on technical evolution and schedule. This move was supported by Apple as well. And so this started Apple’s first major architectural shift in the macintosh line. Amiga did also embrace the Power PC, but by this point Amiga was not a major player in the Computer space and not even run by commodore anymore. For the Atari’s ST line it mostly died before this point. Sun chose to move from 68k to their internal design, the Sparc. And Silicon Graphics moved from the 68k to another RISC CPU, the first RISC CPU, MIPS.
As for the 060, it was used on the Amiga 4000 line, but no Apple product ever used it.
Conclusion
The 16 bit era existed for a short time from 1984 with the release of the original Apple Macintosh until 1986 with the release of the first 32-bit processors in the PC world. But the relevance of these 16 bit machines carried into the early 90’s. By contrast the 32bit era that would rule the world for nearly 3 decades. It wasn’t until 2004 that it would end with the introduction of the AMD Opteron, the first 64-bit X86 compatible CPU built.
So this brief but important time of computing history can be overlooked but served as a critical step in the history of computing. Without the 68k processors it’s hard to say what Intel might have done. It clearly forced them to evolve the x86 line of processors that won out in the long run.
For me the 68k processor holds a special place due to my first computers, Atari ST and Macintosh LCIII both using these processors. I also think that the clean sheet design means it is fairly easy to work with. As easy to work with as early 8 bit designs like the 6502, but with more power.