IBM targets the scale-up market (few big, fast machines) with POWER instead of scale-out (many small, slower machines). Consequentally they are high performance but not particularly tuned for high efficiency, because performance is the more important design goal of the system.
Freescale hasn't made a new low-power Power chip in a while, but... historically speaking, there were a lot of low-wattage / efficiency-focused embedded POWER designs.
I don't know what happened politically between the companies to use ARM instead. But I would imagine that ARM's instruction set was cheaper (or maybe easier) to engineer than Power ISA. Hopefully Freescale engineers can chime in on the discussion, because I'm really just shooting from the hip here.
I would expect most issues to come down to business politics. IBM open sourcing the PowerISA is also a business politics move (I guess they hope to recapture the lost ground in the embedded space).
PowerISA means operating with IBM's ecosystem: GCC, Linux, etc. etc. Remember IBM has merged with RedHat, so there's a lot of promise for Linux support that ARM and RISC-V don't necessarily provide. I think this is a good move.
ARM sells, in addition to ISA licenses, complete designs. I guess that's a big advantage for those that can't afford to develop a full CPU from scratch.
> promise for Linux support that ARM and RISC-V don't necessarily provide
uh, ARMv8 and RISC-V were developed with Linux in mind from the beginning, they didn't even have anything other than Linux/BSD/various-RTOSes, like IBM did with AIX.
Who is writing the RISC-V compiler? If the RISC-V compiler for GCC or CLang messes up, who do you call?
If the Power9 GCC / CLang compilers mess up, you call Red Hat for support. Red Hat / IBM are now the same company, so they'll offer end-to-end services.
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ARM has okay support: the ARM foundation seems to be taking care of their compiler kits / Linux patches / etc. etc. pretty well. But I don't think you can buy an ARM support package from anybody... really.
I think the ARM / Linux ecosystem is still nascent. You get good support through the Rasp. Pi community, and maybe the occasional Android Phone gets a big community around it. But ARM / Linux ecosystem is quite poor outside of Rasp. Pi.
ARM, as a company, is clearly designed as an "embedded" company. It provides the documentation and compilers, but doesn't provide too many OS-level services above that.
> If the Power9 GCC / CLang compilers mess up, you call Red Hat for support
uh, where and when exactly did they offer that? Actually I don't remember anyone anywhere offering commercial support for GCC or LLVM/clang.
Well, I'm not the type of person to look for commercial support for anything ever, but I've heard of several companies that provide support for DBMSes like PostgreSQL. Not so for compilers.
I just googled "gcc commercial support" and the results are the GCC FAQ, a mailing list post about it from 2005 (!), GCC on Wikipedia, "Office 365 GCC" (lol) and so on. Looks like it's just not a thing at all.
IIRC commercial support for GCC is included with some RHEL and SLES subscriptions (probably all except the lowest-cost "desktop"). Red Hat also has a Developer Toolset product that includes a (more recent) complete native toolchain, and SUSE has a similar SLES 12 Toolchain Module / SLES 15 Development Tools Module.
IBM targets both markets. The two variations of POWER9 are literally called scale-up (uses buffered memory) and scale-out (regular DDR4 DIMMs). (Now there's a third one for huge I/O needs…)
