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

[BillPedersen]

On Oct 17, 11:34 pm, glen herrmannsfeldt <g... at ugcs.caltech.edu>
wrote:
> Arne Vajh?j <a... at vajhoej.dk> wrote:
>
> (big snip)
>
> > A VAX is 32 bit because the application use 32 bit virtual addresses.
> > Physical addresses is something else.
> > I can not comment on PDP-11.
> > I seem to recal that physical addresses of later VAX'es were bigger
> > than 32 bit, but 40 bit sounds too much - that would be 4 TB of RAM.
>
> I have sitting here the "VAX Architecture Reference Manual"
> which includes specifications for some VAX.
>
> The last one here is the 8800.  The "Physical address space" is,
> of course, 32 bits, but only 29 bits address installed memory.
> Above that is BI#0, multicast, boot ROM, reserved, node private space,
> reserved, node 0 through node 15, reserved, BI#1 through BI#3, and
> then more reserved.
>
> So up to 512MB of actual memory.
>
> -- glen

The "bitness" of a processor is generally equal to the general purpose
register size.

The Intel 4004 was a 4 bit processor with 12 bits used for
addressing.  It was considered to be a 4 bit processor since its GPs
were 4 bits wide.

The Intel 8008 was an 8 bit processor with a 14 bit address bus.

The PDP-11/20 (the first PDP-11 was a 16 bit processor, byte
addressable to only 16 bits initially, no memory management unit
initially, although the Unibus supported 18 bit addressing, only 16
were used here.

PDP-11/45, the second generation of PDP-11 was also a 16 bit processor
but it had a MMU to access up to 18 bits, so you could have 256KB of
memory, less the 8KB IO space.

PDP-11/70 introduced a MMU which was separated from the Unibus and
provided up to 22 bits memory addressing.  It was STILL at 16 bit
processor.

The PDP-8 was a 12 bit processor, as was the PDP-12/LINC-12.

The PDP-7 (where Unix originated) was an 18 bit processor as was the
PDP-15.  The PDP-7 only had 13 bits for memory addressing, although
there is reference to being able to address up to 32K words of memory
(15 bits) so this implies a primitive MMU (the "Core Memory Extension
Control Type 148).

The PDP-10 and DECSYSTEM 20 were 36 bit processors.

The IBM 360 was designed with 32 bit GPs, except for the Model 20
which was bit of a strange bird with only 16 bit GPs.

Alpha is a 64 bit processor as is I64.

I can find nothing to suggest the "bitness" of a processor is
associated to the addressing.

Bill.