Amiga - a 16bit or 32bit machine?

[Karlos]

From Wiki:

It is 16/32-bit. In other words both. A hybrid more or less. The PPC is pure 32-bit.
The x86 is also a hybrid, so hybrids seem to be the norm.

It's only a hybrid if you regard the physical bus into the outside world as important in the definition. That can vary even on the same processor. As I said previously, you can run a full 68020 on an 8-bit databus if you need to interface only with 8-bit peripherals.

The GPR definition is the best definition, since it overlooks all these considerations and focuses on the capability of the machine. If it has 32-bit general purpose registers that support the regular gamut of operations for 32-bit datatypes, then the machine is best described as 32-bit. The 68000 still falls into this category, even though it was slower at all 32-bit operations (using a 16-bit ALU and internal bus).

[Karlos]

Ok so what made the TI99/4A the first 16 bit micro?

Dunno. You'll have to ask whoever said it was

[Karlos]

If it were, the ALU would have been able to handle 32-bits natively, as the later models did, without resorting to microcode hacks. No doubt the designers intended it to be forward-compatible with 32-bit software, which was a good thought indeed, but the processor was "optimized" (if you will) for 16-bit operations, and 32-bit operations induced cycle penalties in the best case, or wasn't even supported at all in the worst cast (multiply).

The important fact is that is that the 68000 presents a 32-bit programming model to the developer. How it is stitched together internally is never important given that it changes from generation to generation.

Regarding unsupported 32-bit operations 32-bit integer multiplication (with 64-bit product) isn't supported on the 68060 either

[Karlos]

And because they are clocked twice as fast they can still perform 32-bit operations in one clock cycle...

Actually it takes 3 cycles according to the info I read. In the first "fast" cycle, the lower 16-bits are added and ready for forwarding. Then the next 16-bits are added, then finally the condition codes set in a third cycle.

It's pretty stupid really, they could have had a 32-bit ALU and ran it at the same speed, which would have performed better.

Interestingly, a lot of arithmetic operations generated by the compiler use the effective address calculation hardware to evaluate operations, bypassing the ALU all together