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

[Arne Vajhøj]

Neil Rieck wrote:
> On Oct 14, 9:10 pm, Arne Vajhøj <a... at vajhoej.dk> wrote:
>> Neil Rieck wrote:
>>> I hope you guys are correct that this phrase represents a MS s/w
>>> project. However, the use of the phrase IA-128 makes me wonder if
>>> we've seen a glimpse of something coming from Intel.
>>> JF:
>>> Way back in the early 1980's, a DEC instructor told the class that
>>> processor bit size was related to the programmer's view of the general
>>> purpose registers. For example, even though the 8088 had an 8-bit
>>> memory buss, it was (internally speaking) a 16-bit processor. Even
>>> though the 6502 had a few instructions that treated two 8-bit
>>> registers as a 16-bit pair, it was an 8-bit processor.
>>> Obviously things changed when AMD invented AMD64
>>> http://en.wikipedia.org/wiki/AMD64
>>> which forced Intel to respond in kind with similar 64-bit extensions
>>> (a true 64-bit extension of the GP regs) called x86-64 and/or IA-64.
>>> I'm not saying that this is Intel's intention, but Intel could develop
>>> a CPU with 128-bit regs without changing the buss interface unit
>>> (BIU).
>> The general accepted definition of a X bit computer is the size
>> of addresses not the size of registers.
>>
>> There are good practical reasons why they often are identical,
>> but they do not have to be.
>>
>> Even a VAX has somewhat 64 bit general register because q operations
>> could use Rn and Rn+1.
> 
> Instructors at DEC (Kanata, Bedford, Maynard) in the early 80's didn't
> agree with this point of view. At that time, PDP-11 connected to
> memory via anywhere between 18 and 22 bits (depending upon the model)
> but this product line was considered a 16-bit system because of the
> width of the registers. Likewise with VAX, we saw lots of schemes to
> address more memory (well over 40-bits IIRC) but VAX was always
> considered a 32-bit system.

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.

Arne