As far as binaries go you can still target the COM instruction set with the compiler and the same binary will run on any 32/64 PPC up to the latest POWER chips.

I was wondering if someone could come up with a POWER9-based accelerator board for PPC-based Macs.

Obviously niche, but most amusing. Imagine a 48-core 5 GHz MacPro G5.

it'd probably totally be.. possible - to get OS X to boot on a POWER9 system. There seems to be more interest in getting Classic OS to run on modern hardware though

I'd totally want my Mac work environment running on a dual socket POWER9 workstation.

Mac System 9 running on modern hardware, not in an emulator?

Now the web browser can crash the entire system an order of magnitude faster!

That said I love the idea from the perspective of a wonderful hack, but I truly hope no one actually has a use case where running classic Mac OS on modern hardware makes sense.

The 601 was pre-standard, so I'd imagine that there would be a huge difference.

It had the first implementation of the multiprocessing unit, and lacked the load/store and registry units of all the later processors.

Bit like comparing a 8086 to the latest and greatest, still have support for the instructions of the time, but been lots of additions since. At least comparing the ISA level.

Didn’t PowerPC have some unique extensions that distinguishes it from the the POWER CPUs?

Yeah, but Power3 and onward actually implement the PowerPC ISA so the differences are smaller than they appear.

No. Not even remotely close. The 8086 was an 8 bit processor with some 16 bit extensions and segment registers. This is worlds different than 32 bit x86. They're worlds apart.

The PowerPC 601 is functionally quite similar to modern 32 bit PowerPC.

The 8086 was a 16 bit CPU. Every register is 16 bit as is the internal and external data bus (the address space is actually 20 bits, but that's a different issue).

...except it barely more of a 16 bit processor than a Z80, and had 8 bit instructions, extendable to longer, like the Z80. Aside from the 20 bit addressing and 16 bit offset, the 8088 and Z80 were equivalent.

Or should we call the Z80 a 16 bit processor?

> Or should we call the Z80 a 16 bit processor?

Z80 is classified as an 8-bit processor because it has an 8-bit internal data bus to the register file.⁽¹⁾

This is visible in instruction timings: 16-bit INC BC takes longer than 8-bit INC B because the 16-bit register access takes two internal data cycles compared with one internal cycle for 8-bit.

Intel 8086 is classified as a 16-bit processor because it has a 16-bit internal data bus to the register file.

This is visible in instruction timings: 16-bit register operations generally take the same time as 8-bit register operations.⁽²⁾

⁽¹⁾ Trivia: Z80 also has a 16-bit internal address bus and 4-bit ALU.

⁽²⁾ Actually 8-bit INC AL takes longer than 16-bit INC AX, opposite way around from Z80. But that's because of a longer instruction encoding, not architecture. MOV AL,BL takes the same time as MOV AX,BX.)

It's been more than a decade since I wrote any ppc asm and I don't remember much.

I imagine they extended the ISA to 64 bits and maybe that was an opportunity for further ISA changes?