[Info-vax] OT: IA-128 ???

[glen herrmannsfeldt]

Arne Vajh?j <arne at vajhoej.dk> wrote:
(snip)
 
< The general accepted definition of a X bit computer is the size
< of addresses not the size of registers.

I suppose so, but mostly on machines where the register size
equals the address size.  Also, do you mean virtual address
size or physical address size?
 
< There are good practical reasons why they often are identical,
< but they do not have to be.

And for those machines where they aren't the question is open.
Consider processors like the 680x0 or some CRAY machines with A 
registers (for addressing) and D registers (for data) that might 
have different sizes.
 
< Even a VAX has somewhat 64 bit general register because q operations
< could use Rn and Rn+1.

That pretty much doesn't count unless at least add, subtract,
multiply, and divide can be done on the full size.  

Motorola liked to call the 6809 the missing link between 8
and 16 bit processors.  Among others, it had a fairly complete
set of addressing modes including 16 bit index registers.
Also, an 8 by 8 multiply with 16 bit (unsigned) product,
pretty unusual as 8 bit processors go.

The 8086 has a 20 bit address space but was not considered
a 20 bit processor.  IA32 processors starting with the PentiumPro
have a 36 bit physical address bus, but aren't 36 bit processors.

-- glen