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Comment by jagrsw | Hacker News Reader

Since the 1990s PowerPC/POWER has been touted as viable alternative to the x86 architecture. Initially, they gained traction through PowerMacs and Amigas with accel-cards, as well as via PPC versions of Windows and OS/2. Next, they aimed to compete in the cloud, where ARM eventually outpaced them.

I have first-hand experience porting https://phoenix-rtos.com/ to PowerPC back in the early 2000s and it's a very sane CPU arch (in comparison to x86). However, it's evident that POWER lags behind x86, ARM, and now RISC-V, both in terms of use and public attention.

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> it's a very sane CPU arch (in comparison to x86)

Anything is sane compared to current x86. Each generation is an added layer of complication on top of the previous one and it's been going on since the late 70's.

I bet PowerPC still has some 68000 stuff into it.

If anything x86 is a proof that evolution works better in market adoption than nuking everything, specially when not every company cares about the bazaar, only their cathedrals.

> I bet PowerPC still has some 68000 stuff into it.

You'd lose. There were two platforms who made that jump, but the architectures have no lineage in common at all.

Wild in retrospect, but the original Apple plan for the PowerPC transition was to have no backward binary software compatibility at all!

Interesting and surprising! Is there a source for this?

There seems to have been a lot of work on emulation by Gary Davidian from an early stage - starting with the AMD 29000 then 88k and then finally on PowerPC - according to his CHM oral history.

The version of this story I heard first comes from the (absurdly fun, if you’re into that sort of thing) 65scribe YouTube channel’s video on the PowerMac 8100:

https://youtu.be/XYWp_R33mDs?si=4czECGOaHiM-MQqt

Roughly lines up with the history recounted here:

https://lowendmac.com/2014/ibm-apple-risc-and-the-roots-of-t...

Apple was planning to go with a radical new design, breaking with the past in both software and hardware, but Gary Davidian & co. saved them from their own foolishness via a skunkworks project that actually could ship.

Many thanks! Yes, all fits together.

By complete co-incidence I have a blog post on the various Mac CPU transitions in draft that should be out tomorrow.

One mildly amusing point, which I don't think is mentioned in either link is that the Cognac project was so called because the surname of John Hennessy, of Stanford RISC and MIPS fame, is also, of course, the name of a brand of Cognac.

There's one register called CCR on m68k and CR on PPC, so that's probably not an accident ;)

The term "condition-code register" predates by decades both the Motorola MC68000 (1979) and the IBM POWER (1990). It was a term used in many unrelated computers.

Already in 1964, in IBM System/360, the condition-code was a part of a bigger register, the "processor status word". The terms are much older than that.

Also in MC68000, the CCR is a part of the bigger status register, which, unlike the CCR, can be accessed only by privileged programs.

In POWER, the condition register also holds only the condition-code part of the status, but it has room for 8 groups of condition codes, to allow high speed even for cheaper in-order CPUs, which do not have register renaming (where otherwise a shared condition-code register would prevent the concurrent execution of instructions).

Yeah, in practical implementations the 32-bit Power condition register is more like eight four-bit ones, and lots of code will run compares in parallel to different fields. It's one of the architecture's notable strengths.

I don't know if it was the 68000 but Apple demanded that when they adopted POWER, Motorola could still supply chips. But Motorolas core couldn't be made to run POWER. So PowerPC is basically a merge between IBM Power core and Motorola's next generation core.

Is there anything standing in the way of people making open source cores that would be binary compatible with a modern POWER core? I love RISC-V's inroads in embedded, research, and education but I'm a bit skeptical of it succeeding in application cores in its current form and open POWER cores might be another road to open source hardware.

That's pretty much what this is.

>but I'm a bit skeptical of it succeeding in application cores in its current form

Be a little patient. A bunch of very high performance application cores are hitting the market next year.

Sure judgement can be delayed till then.

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