Why did the Motorola 68000 processor family fall out of use in personal computers in the 21st century?

Question

In the '80s and '90s the Intel x86 and Motorola 68000 families were the two leading microcomputer architectures in the 16-bit/32-bit personal computer scene. The 68000s were even preferred by the purists because of its orthogonal instruction set. The Intel x86 family, although always the market leader, has been criticized for its non-orthogonal instruction set and segmented addressing.

When the Macintosh line switched to PowerPC, the Motorola 68000 family began to disappear as a contender for newly designed personal computers outside the “Wintel” ecosystem. New contenders, such as the PowerPC, ARM and MIPS, take the 68000 family’s place.

I cannot find on the internet the reason why the 68000 family fell out of favor in the personal computer market.

Can someone explain this or point me in the direction of the answer?

Answer 1

The Apple-IBM-Motorola alliance was created in 1991 to compete with the Windows/Intel market. Its main successes were the creation of the PowerPC instruction set, derived from IBM's POWER architecture, and Apple's Power Macintosh line of computers.

IBM originated the idea, having seen that Windows on Intel was out-competing OS/2, and wanting to avoid being dependent on Intel. Apple joined it, seeing the chance to grow out of their existing markets, and Motorola presumably saw it as a successor to 68000, having failed comprehensively with the MC88000.

While the 68000 was used in the Macintosh series, Atari STs and Amigas, all of which sold in large numbers, all the operating systems involved were quite different, so there was no unified software base. That meant there wasn't the sustained demand for 68000 that could have paid for chip development on the scale required to keep it competitive with x86. The engineering workstation market had started with the 68000, but had already switched to RISC before AIM was created.

Answer 2

The 68k family instruction set, as elegant as it appeared to the casual assembler programmer (been there), had several flaws that made it very difficult to get fast in hardware. Out of order or superscalar execution were very, very difficult to implement.

• Over-complex addressing modes, especially the indirect one introduced with 68020: when combined with virtual memory made it theoretical possible to get up to 16 page faults in 1 instruction (move long indirect with displacement and shifted index from an odd address touching 2 pages etc.). These indirect addressing modes were the first to be removed when defining the Coldfire ISA.
• Exposure of the pipeline internals on traps and exceptions: the idea was that on a trap, the instruction could be resumed after fixing the error cause. This made it very difficult to get performance out of the kernel as it wrote more and more data to the stack at each generation, and it also limited the internal state that could be saved. x86 was much more pragmatic and just restarted the cancelled instruction from start.
• Compatibility between successive family members was not as good as in intel CPUs. If you want to compile a program that runs on 68000 and on any of 680[2346]0 you will lose a lot of features on the side.

There is the famous newsgroup post from John Mashey explaining the fundamental issue with the 68k ISA in comparison to other ISAs of that time.

Answer 3

Motorola stopped investing in MC68000 family when everyone thought that RISC was the future and that CISC CPUs would be soon non competitive. So it switched to PowerPCs.

Even Intel thought this and developed RISC CPUs (i860, i960...). Intel reluctantly continued investing in x86.

For Motorola, it was probably true, the last version, MC68060 was competitive with Pentium but it was quickly surpassed because of Intel manufacturing superiority allowing lower dissipation, higher frequencies. Switching to simpler RISC CPUs could allow to stay in the race.

Now, the difference between RISC and CISC (eg x86) is less relevant performance-wise due to the possibility of putting 100 times more transistors on a die.

Answer 4

When the Macintosh line switched to Power PC, the Motorola 68000 family begun to disappear

It's been rather the other way around. Apple switching was a result of Motorola losing the race.

New contenders, such as the Power PC, ARM and MIPS take the 68000 family’s place.

Not really - also you forget the NS32k family going away at the same time, being maybe less visible but at least as successful as the 68k.

I cannot find in the internet the reason why the 68000 family fell out of favor in the personal computer market.

Cost on either side:

• Motorola wasn't able to keep up investment to improve their CPUs the same way that Intel did
• Resulting CPUs were considerably more expensive than Intel's offering.

This is not only true at upper end offerings with '060 vs. Pentium but even more for embedded. Basic 80(1)88 based systems could be delivered at considerable lower development and production cost.

Answer 5

Motorola lost the race to 32 bit computing from a simple engineering mistake. In the era when the 68k and x86 were very popular, the shift to 32 bit CPUs was a race to mass production. No question the 68020 was a cleaner design and almost destined to be the no. 1 choice for new machines. Friends of mine paid around $400 at the time for early 68020 chips to build test boards. X86 at the time was hopelessly behind. BUT, the first iteration of the 68020 had pushed the design parameters of the chip process to the point that yields were appalling. Every chip sold at a loss. Motorola then had to redesign all the masks which was an 18 month engineering exercise. 18 months was the window that let x86 get ahead in the market and that was the end of the 68k family's dominance. Shame

Answer 6

I was at Intel from the late 80’s to the early 00’s first as a CPU architect then running various design teams and research teams. Prior to Intel I was an architect/designer of systems using 68K, x86, and custom CPU’s.

Readers of this forum are mostly technologists and will tend to answer from a technology-centric perspective (as the saying goes: To a carpenter with a hammer, everything looks like a nail). The reality is that market outcomes are the result of multiple inter-dependent factors. Technologies are only one factor and frequently not the most important. These factors include market participants (buyers and sellers), market structure (supply chains, sales channels), as well as technologies. All of these factors rest on a foundation of organizational execution and economic behavior.

When assessing market outcomes one needs to understand what is being purchased, who is making the purchase decision, and what their value propositions are. The question was about CPU’s but buyers weren’t buying “CPU’s”, they were buying “boxes” containing CPU’s and other components such as DRAM, disks, and operating systems.

Why were they buying boxes? To run application software – which over the time period in question was bought as a product (a binary), not as a service (SaaS). Binaries were compiled to a particular CPU instruction set and OS API – changing either would require buyers to pay for a new binary. To maximize the return of acquisition cost these binaries were re-used over multiple box/CPU generations.

In approximate order of units shipped, the ecosystems using microprocessors in the late 80’s were: Wintel PC, Apple, Sun Microsystems workstations, other workstation vendors (e.g. Apollo, SGI), and a smattering of microprocessor-based mini-computers. Except for the Wintel PC ecosystem, all used 68K.

In 1986 Sun replaced the 68K with SPARC, their home-grown RISC. In 1994 Apple replaced the 68K with PowerPC. In the 90’s SGI moved to MIPS. Other 68K vendors were either acquired or went out of business. Each vendor changed CPU’s for different reasons. Sun wanted to move to RISC – no doubt influenced by Bill Joy who joined Sun from Berkeley where a RISC project was ongoing. By the 90’s, Apple had become worried about Motorola’s ability to keep pace with Intel in both performance and power (Apple threw a bone to Motorola by including them the AIM Alliance making PowerPC’s).

As the installed base of an instruction set or OS API increases, the incentive for software developers to target their binaries to these interfaces also increases – to amortize their upfront cost of development over a larger number of units shipped. This instantiates a feedback loop: Increasing ecosystem volume attracts more apps which increases demand for that ecosytem. Exacerbating this feedback loop was the fact that x86 volume was overhwelmingly concentrated on a single OS API (DOS then Windows) while 68K volume was split over multiple, incompatible, OS API’s (Apple, Sun, et al).

The profit from CPU generation N needs to pay for all the components of generation N+1: CPU development, fab process development, and at least one fab. The underlying economics of fabs are such that, as soon as a new fab process is ready, there should be a new CPU design ready to take advantage of the higher transistor budget enabled by that process and begin amortizing the very large upfront cost of building a fab. Adding to this was the fact that Intel’s yields were significantly higher than other CPU vendors.

One of the largest causes of 68K’s demise was Motorola’s execution relative to Intel. It was clearly the case that over the course of the 90’s the cadence at which Motorola shipped new CPU’s fell relative to Intel. These CPU execution cycles destructively (Motorola), or constructively (Intel), resonated with the underlying economics of silicon fabs, ecosystem platform volumes, and app development. Motorola’s CPU execution descended a vicious economic cycle while Intel’s ascended a virtuous economic cycle.

These are the broad strokes. There’s more detail here but this answer is already getting long.

Answer 7

This was purely economics. By about 1988 the ready availability of IBM AT clones had the effect of pushing the price of support hardware- including cases, discs etc.- down enormously, and even on the '286 there were UNIX variants that demonstrated that such things were possible. The '386, when introduced, exploited that, and from that point onwards it became a race between what Intel- with a growing income- and Motorola et al.- with static incomes- could do with the available semiconductor technology.

By about 1995 Intel's price/performance ratio was unassailable, and graphics accelerators which could operate in conjunction with PC hardware were starting to erode the market for specialist workstations.