Happy Birthday VAX 11/780 - test-drb@ccmp.vtda.org

26 Oct 2010

On 10/26/10 04:20, Roger Holmes <roger.holmes at microspot.co.uk> wrote:

...
   >  From: Mr
Ian Primus<ian_primus at yahoo.com>
 >  And glaringly so. To say that the 11/780 is the first 32 bit machine is just silly.
Prime had a 32 bit machine in 1972. And I know that there were others - but the Prime is
the machine that I know the best:)  I think I'm right saying the Manchester
'Baby' had a 32 bit word in 1948, actually 32 of them on one Williams tube.
However as it was a serial machine the data path to memory was actually one bit wide so it
depends how you define bit size, but I was taught it was the largest addressable unit of
memory and by that definition it had a 32 bit word. 
What does "largest addressable unit of memory" means? I totally fail to 
understand that. Sounds like "the largest memory chip that can be 
utilized", but that can hardly be the meaning.

...
  There was talk of the VAX design being the inspiration
for the Motorola 68k. Isn't it more likely that the PDP11 influenced the design of
both the VAX and the 68k? 
That the PDP-11 influenced the VAX there can be no doubt about.
The the PDP-11 influenced the 68K seems very probable when looking at 
the architectures, but that is guessing on our part.

William Donzelli<wdonzelli at gmail.com> write:
...
   >  There
was talk of the VAX design being the inspiration for the Motorola 68k. Isn't it more
likely that the PDP11 influenced the design of both the VAX and the 68k?  Big
microcoded CISC was the dominant thinking in computer architecture
 at the time, so it is really hard to say that X influenced Y. 
Well, the fact that DEC explicitly stated that the VAX would be like the 
PDP-11, but extended to 32 bits seems like an obvious statement that the 
PDP-11 influenced the VAX. Not to mention the fact that they used the 
same peripherial buses, and at VMS V1, most of the applications were 
just the RSX programs moved straight over. Oh, and don't forget the 
compatibility mode in the VAX, which made it execute PDP-11 code. :-)

As for the 68K, we are making more of a guess, but it seems like a 
fairly educated guess that the 68K was inspired by the PDP-11 (although 
I'd say the 68K is way inferior to the PDP-11...)

	Johnny