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It was pretty commonly accepted at the time that the 68000 was a "16-bit CPU" because of its ALU and data bus width, despite the 32-bit being clearly ISA. The S

by wk_end 2y ago

It was pretty commonly accepted at the time that the 68000 was a "16-bit CPU" because of its ALU and data bus width, despite the 32-bit being clearly ISA. The Sega Mega Drive/Genesis, for instance, is always referred to as a 16-bit console, even having it embossed right on its shell. The technical truth is that using a single number to describe the "bits" of a CPU is going to be inadequate in many cases (including this) so this was a choice by marketing. I'm not sure why that was the case; one would think marketers would have rushed to use the biggest, most impressive sounding numbers available. Maybe they wanted to keep something in reserve for when the 68020 came down the pipe? Maybe they were scared of being criticized or even sued for false advertising since the chip wasn't "truly" 32-bit?

ddingus 2y ago
Like the 6809 is an 8 bit chip? I buy that argument. My personal reference is the 68K is a 16 bit chip, like the 6809 is an 8 bit chip. Moto just made really great CPUs at that time. And the fact is Moto did well by making sure the future was clear for 32 bits. Mostly just a hardware change. (Except for people who stuffed info into those upper address bits. Oops!)
guenthert 2y ago
Well, I don't think there was any consensus. Atari played on this with the "ST" (for sixteen/thirty-two) product label. From the software side it was 32bit. The flat, huge (at that time) address space made things so much easier (compared to the awful segmentation of the Intel CPUs then). That the ALU was just 16bits meant that some operations took longer than one would have liked, but was otherwise of no concern. No "far pointers" or any such crutches.
- kstrauser 2y ago
  That's how I see it. As a developer, you still used 32-bit math operations in assembly and the CPU executed them as a series of 16-bit ops. The details are abstracted away. IMO, that made it 32 bits. By analogy, SATA is a serial protocol, but you wouldn't ordinarily refer to it as a 1-bit bus.

by wk_end 2y ago

ddingus 2y ago

Like the 6809 is an 8 bit chip? I buy that argument. My personal reference is the 68K is a 16 bit chip, like the 6809 is an 8 bit chip. Moto just made really great CPUs at that time. And the fact is Moto did well by making sure the future was clear for 32 bits. Mostly just a hardware change. (Except for people who stuffed info into those upper address bits. Oops!)

guenthert 2y ago

Well, I don't think there was any consensus. Atari played on this with the "ST" (for sixteen/thirty-two) product label. From the software side it was 32bit. The flat, huge (at that time) address space made things so much easier (compared to the awful segmentation of the Intel CPUs then). That the ALU was just 16bits meant that some operations took longer than one would have liked, but was otherwise of no concern. No "far pointers" or any such crutches.

kstrauser 2y ago
That's how I see it. As a developer, you still used 32-bit math operations in assembly and the CPU executed them as a series of 16-bit ops. The details are abstracted away. IMO, that made it 32 bits. By analogy, SATA is a serial protocol, but you wouldn't ordinarily refer to it as a 1-bit bus.