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I keep reading here great things about the 68k. What made Motorola diverge from it and invest in a whole new arch (88k) rather than keep pushing the 68k line? I

I keep reading here great things about the 68k. What made Motorola diverge from it and invest in a whole new arch (88k) rather than keep pushing the 68k line? Intel succeeded in evolving x86 despite it being an originally subpar design, surely the 68k could have been taken further more easily?

ghaff 3y ago
At some point (maybe the 68040?), the 68K line started to decline in popularity and there was a significant contingent of the industry that was convinced that RISC was the future (not that they were really wrong). The big Unix system companies were mostly doing their own RISC designs and Motorola figured that they had a significant market in the second-tier players like Data General that weren't going to do their own RISC designs. Intel did try to do RISC unsuccessfully with the i860--which also had some sort of VLIW mode, which makes their later Itanium even harder to understand.
cmrdporcupine 3y ago
Lower sales. Bad management. And there was a consensus at that point that CISC was a dead-end and RISC was the future. Also, they did in fact take the 68k further (ColdFire) but too late, long after they had pushed their serious customers to PowerPC. Intel was making enough coin from x86 that they were reluctant to EOL it in favour of something RISC. Not that they didn't try. Multiple times (Itanium being the worst, though much later). But each time their replacement failed to ignite, and Intel pulled back from the brink and they pushed something that was a noticeable incremental improvement while keeping backward compatibility. And with the Pentium & the ISAs that followed they just seemed to pull a rabbit from a hat. They made the x86 CISC architecture scale in a way that pundits at least? didn't seem to think was possible. Motorola didn't invest in time in doing for 68k what Intel did for x86 with the Pentium. And they screwed over their customers as a result. They basically told everyone (Apple, NeXT, various workstation makers, etc.) to go to 88k. 88k was an architectural failure. So then they did PowerPC along with IBM and others. And people who used 68k previously either went PowerPC (Apple) or rolled their own RISC (Sun with SPARC, HP with PA-RISC, etc.) or just left the market entirely (Apple, Commodore). ColdFire is roughly to the 68k what Pentium II or so was to the x86 line. It's actually quite nice. They dropped a couple things from 68k but it's about 90% compatible, and can do a very effective software emulation to make itself 100%. But it got pushed basically only as a microcontroller or specialist (routers, ethernet switches, etc.) architecture. You can still buy them from NXP I believe. These days I don't like big-endian. And the separate address vs data registers seems weird now. But the 68k instruction set was overally very nice. I do imagine sometimes an alternate timeline where Motorola had rolled ColdFire out sooner as an MPU line for consumer stuff and Apple, etc. had used that instead of going PowerPC. I wonder what a 64-bit 68k would have looked like. IMHO Apple wasted a whole pile of engineering years getting MacOS classic to port over natively to PowerPC. It was extremely unstable and large parts were emulated 68k code for years. It might have saved them some unprofitable years, who knows? They seem to have finally learned the lesson and they own their own CPU now.
- temac 3y ago
  > And with the Pentium & the ISAs that followed they just seemed to pull a rabbit from a hat. They made the x86 CISC architecture scale in a way that pundits at least? didn't seem to think was possible. The Pentium was not great, not terrible. IIRC 2 ways superscalar in-order, quite faster than the 486 (also because of caches, better memory, faster and wider FSB, way better latencies for tons of instructions) but it would not have been enough if Intel had tried to just make it evolve slowly. Of course at the time and taking price and competition into account, it was quite good to make faster PCs. But by itself it only showed a limited capability for scaling x86. The Pentium Pro was the uarch that showed that scaling was possible. Even if they have been deeply refined across the years and generations (putting NetBurst appart, of course), most of the technics it introduced in the x86 world are still a foundation of how the current generation x86 cores work. The rabbit that came out of the hat was the result of quite a number of years of work, most of it parallel to the P5 dev. The Pentium II consolidated that with better support for consumer software of the time (with still copious amount of 16-bit code), and, logically, marketing for consumer hardware (with manufacturing progress and tricks allowing a price not too high).
  - labcomputer 3y ago
    > The Pentium was not great, not terrible. IIRC 2 ways superscalar in-order, Eh, I don't agree. Look at the other superscalar microprocessors available around the same time: * POWER (1990) * Alpha 21064 (1992) * PA-RISC 7100 (1992) * Pentium (1993) * POWER2 (1993) * MIPS R8000 (1994) * PA-RISC 7200 (1995) * UltraSparc (1995) * Alpha 21164 (1995) So, first of all, all of these are in-order processors. Out of order execution didn't come until later ('95 for PA-8000, '96 for R10k and Pentium Pro and '98 for Alpha 21264 and Power3). Second, all of the RISC superscalar processors prior to the Pentium are also (technically) dual issue. But Pentium did something unique: It can issue two integer instructions in the same cycle. Before that, all the others could issue only one instruction of a given type (load/store, int, and fp) per cycle. In other words, while they may be "dual issue", your instruction stream needs a mix of those types to get any benefit from multi-issue on those early implementations. In terms of having 2x execution units of the same type: POWER2 got there later in 1993, but was not a single-chip processor, followed by R8000 (also multi-chip), PA-7200 and 21164. That's why Pentium had pretty good integer benchmarks, even while it was getting crushed on floating point compared to RISC.

ghaff 3y ago

At some point (maybe the 68040?), the 68K line started to decline in popularity and there was a significant contingent of the industry that was convinced that RISC was the future (not that they were really wrong). The big Unix system companies were mostly doing their own RISC designs and Motorola figured that they had a significant market in the second-tier players like Data General that weren't going to do their own RISC designs. Intel did try to do RISC unsuccessfully with the i860--which also had some sort of VLIW mode, which makes their later Itanium even harder to understand.

cmrdporcupine 3y ago

Lower sales. Bad management. And there was a consensus at that point that CISC was a dead-end and RISC was the future. Also, they did in fact take the 68k further (ColdFire) but too late, long after they had pushed their serious customers to PowerPC. Intel was making enough coin from x86 that they were reluctant to EOL it in favour of something RISC. Not that they didn't try. Multiple times (Itanium being the worst, though much later). But each time their replacement failed to ignite, and Intel pulled back from the brink and they pushed something that was a noticeable incremental improvement while keeping backward compatibility. And with the Pentium & the ISAs that followed they just seemed to pull a rabbit from a hat. They made the x86 CISC architecture scale in a way that pundits at least? didn't seem to think was possible. Motorola didn't invest in time in doing for 68k what Intel did for x86 with the Pentium. And they screwed over their customers as a result. They basically told everyone (Apple, NeXT, various workstation makers, etc.) to go to 88k. 88k was an architectural failure. So then they did PowerPC along with IBM and others. And people who used 68k previously either went PowerPC (Apple) or rolled their own RISC (Sun with SPARC, HP with PA-RISC, etc.) or just left the market entirely (Apple, Commodore). ColdFire is roughly to the 68k what Pentium II or so was to the x86 line. It's actually quite nice. They dropped a couple things from 68k but it's about 90% compatible, and can do a very effective software emulation to make itself 100%. But it got pushed basically only as a microcontroller or specialist (routers, ethernet switches, etc.) architecture. You can still buy them from NXP I believe. These days I don't like big-endian. And the separate address vs data registers seems weird now. But the 68k instruction set was overally very nice. I do imagine sometimes an alternate timeline where Motorola had rolled ColdFire out sooner as an MPU line for consumer stuff and Apple, etc. had used that instead of going PowerPC. I wonder what a 64-bit 68k would have looked like. IMHO Apple wasted a whole pile of engineering years getting MacOS classic to port over natively to PowerPC. It was extremely unstable and large parts were emulated 68k code for years. It might have saved them some unprofitable years, who knows? They seem to have finally learned the lesson and they own their own CPU now.

temac 3y ago
> And with the Pentium & the ISAs that followed they just seemed to pull a rabbit from a hat. They made the x86 CISC architecture scale in a way that pundits at least? didn't seem to think was possible. The Pentium was not great, not terrible. IIRC 2 ways superscalar in-order, quite faster than the 486 (also because of caches, better memory, faster and wider FSB, way better latencies for tons of instructions) but it would not have been enough if Intel had tried to just make it evolve slowly. Of course at the time and taking price and competition into account, it was quite good to make faster PCs. But by itself it only showed a limited capability for scaling x86. The Pentium Pro was the uarch that showed that scaling was possible. Even if they have been deeply refined across the years and generations (putting NetBurst appart, of course), most of the technics it introduced in the x86 world are still a foundation of how the current generation x86 cores work. The rabbit that came out of the hat was the result of quite a number of years of work, most of it parallel to the P5 dev. The Pentium II consolidated that with better support for consumer software of the time (with still copious amount of 16-bit code), and, logically, marketing for consumer hardware (with manufacturing progress and tricks allowing a price not too high).
- labcomputer 3y ago
  > The Pentium was not great, not terrible. IIRC 2 ways superscalar in-order, Eh, I don't agree. Look at the other superscalar microprocessors available around the same time: * POWER (1990) * Alpha 21064 (1992) * PA-RISC 7100 (1992) * Pentium (1993) * POWER2 (1993) * MIPS R8000 (1994) * PA-RISC 7200 (1995) * UltraSparc (1995) * Alpha 21164 (1995) So, first of all, all of these are in-order processors. Out of order execution didn't come until later ('95 for PA-8000, '96 for R10k and Pentium Pro and '98 for Alpha 21264 and Power3). Second, all of the RISC superscalar processors prior to the Pentium are also (technically) dual issue. But Pentium did something unique: It can issue two integer instructions in the same cycle. Before that, all the others could issue only one instruction of a given type (load/store, int, and fp) per cycle. In other words, while they may be "dual issue", your instruction stream needs a mix of those types to get any benefit from multi-issue on those early implementations. In terms of having 2x execution units of the same type: POWER2 got there later in 1993, but was not a single-chip processor, followed by R8000 (also multi-chip), PA-7200 and 21164. That's why Pentium had pretty good integer benchmarks, even while it was getting crushed on floating point compared to RISC.