Happy Birthday VAX 11/780 (influence of)

Brent Hilpert hilpert at cs.ubc.ca
Thu Oct 28 13:42:44 CDT 2010

On 2010 Oct 28, at 10:51 AM, Chuck Guzis wrote:
> On 28 Oct 2010 at 13:20, William Donzelli wrote:
>> I was initially thinking about just the hardware architecture when the
>> machines were being designed, not the software aspect, nor what the
>> machines did (or influenced) after they were released. The
>> aforementioned memory mapped I/O, for example.
> Not to be too much of a wet blanket, but how many of those DEC-unique
> innovations (even if you manage to assert that they originated with
> DEC) persist in today's hardware?  Do modern PCs use memory-mapped
> I/O?  The 68K, but for some Freescale relics, is history.
> Major innovations, such as virtual memory and orthogonal instruction
> sets and hardware-implemented stacks preceded the PDP-11.

How about the notion that the PDP-11 was where several prior but 
then-topical innovations coalesced into one machine/architecture?

The VAX was riding on the coattails of the market success of the -11 
and provided existing PDP-11 installations with increasing demands with 
a way forward, and it grew from there. That's a bit of a tautology, but 
it is to say it did exactly what it was designed and marketed for.

On the topic of memory, I would agree with Johnny about "virtual 
addresses", but differ on "virtual memory": virtual memory to me has 
always meant demand-paging where the RAM address-space seen by the user 
can be larger than the physical RAM, distinct from the simple mapping 
of addresses, but the use of the term is a matter of definition.

> Perhaps the major contribution of the PDP-11 and VAX was that they
> were comparatively cheap for the processing power.

.. the right product, at the right time, at the right price, from an 
established and reliable manufacturer/source.

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