Re: Whether something is RISC or not (Re: PDP-8 theology, not Concertina II Progress)

On 16/04/2024 02:35, Lawrence D'Oliveiro wrote:

On Sun, 14 Jan 2024 14:30:51 -0500, EricP wrote:
 

Furthermore, the address and data registers and buses are 16 bits and
the high 16-bits are shared ...

 No, in the 68000 family the A- and D- registers are 32 bits.
 If you compare the earlier members with the 68020 and later, it becomes
clear that the architecture was designed as full 32-bit from the
beginning, and then implemented in a cut-down form for the initial 16-bit
products. Going full 32-bit was just a matter of filling in the gaps.

Yes, the 68000 was designed to have full support for 32-bit types and a 32-bit future, but (primarily for cost reasons) used a 16-bit ALU and 16-bit buses internally and externally.  Some 68000 compilers had 16-bit int, some had 32-bit int, and some let you choose either, since 16-bit types could be significantly faster on the 68000 even though the general-purpose registers were 32-bit.