Comment by adrian_b
4 hours ago
Motorola had made a few design mistakes, like adding memory indirect addressing in MC68020, which were removed much later, in the ColdFire Motorola CPUs.
But Intel had made much more design mistakes in the x86 ISA.
The truth is that the success of Intel and the failure of Motorola had absolutely nothing to do with the technical advantages or disadvantages of their CPU architectures.
Intel won and Motorola failed simply because IBM had chosen the Intel 8088 for the IBM PC.
Being chosen by IBM was partly due to luck and partly due to a bad commercial strategy of Motorola, which had chosen to develop in parallel 2 incompatible CPU architectures, MC68000 intended for the high end of the market and MC6809 for the low end of the market.
Perhaps more due to luck than due to wise planning, Intel had chosen to not divert their efforts into developing 2 distinct architectures (because they were already working in parallel at the 432 architecture for their future CPUs, which was a flop), so after developing the 8086 for the high end of the market they have just crippled it a little into the 8088 for the low end of the market.
Both 8086 and MC68000 were considered too expensive by IBM, but 8088 seemed a better choice than Z80 or MC6809, mainly by allowing more memory than 64 kB, which was already rather little in 1980.
In the following years, until 80486 Motorola succeeded to have a consistent lead in performance over Intel and they always introduced various innovations a few years before Intel, but they never succeeded to match again Intel in price and manufacturing reliability, because Intel had the advantage of producing an order of magnitude more CPUs, which helped solving all problems.
Eventually Intel matched and then exceeded the performance of the Motorola CPUs, despite the disadvantages of their architecture, due to having access to superior manufacturing, so Motorola had to restrict the use of their proprietary ISAs to the embedded markets, switching to IBM POWER for general-purpose computers.
Analysis of issues in making more performant 68k and VAX are major part of what led to RISC development, with complex addressing (even in earliest 68000) being part of the problem. People think of x86 as CISC when reading about CISC vs RISC, but x86 was not much of a consideration when industry was switching to RISC-style designs - it was hitting walls on complex ISAs, especially VAX (which was allowed to live for way too long), but also to an extent 68k.
N.b. 68000 was supposed to be a 16bit extension of 6800, which among others resulted in hilarious two layers of microcoding.
AS for IBM PC, 68000 had major flaw of being newer while 8086 had been available for longer and with second sources - 68000 was released at the same time as reduced capability 8088, while equivalent reduced capability model for 68k arrived in 1982.