[Info-vax] DEC Large Systems

[Arne Vajhøj]

On 6/27/2019 7:50 AM, Bill Gunshannon wrote:
> Another question born out of curiosity.
> 
> I was looking at a catalog called Large Systems Software
> Referral Catalog (Fourth Edition) from 1984.
> 
> It lists DECsystem-10, DECSYSTEM-20 and VAX. (notice the
> curious spellings used by DEC themselves  :-)
> 
> What exactly did the VAX offer or what shortcomings were
> seen in the 10 and 20 that caused VAX to become the hero
> and the other large systems to go away?

This is before my time.

But my understanding is that the old boxes had a memory
limit of 4 MW while VAX had larger byte address space
(32 bit virtual and 24/30/32 physical).

So DEC either had to make significant changes to the
old architecture or go with a new architecture.

We know what they chose. Could they have chosen different: likely.
That is like asking if VAX could have been extended to 64 bit. It
probably could, but DEC chose to go with Alpha.

Arne