[Discuss] Whence distributed operating systems?

[richard.pieri at gmail.com (Rich Pieri)]

On 4/28/2016 8:30 PM, Bill Bogstad wrote:
> Can you clarify what you mean by "shared via software"?   Did the
> virtual memory system, page fault data from remote QBBs as needed or
> was there a fibre bus transaction every time a local process accessed
> remote memory?   I understood your original note to mean that from a
> programs perspective it could allocate/use memory in other QBBs
> transparently (except for possible performance differences).

That was the idea, yes. I don't know the low-level details of how it was
supposed to work beyond being something akin to Memory Channel via software.

> The fact
> that this was done via a fibre data bus vs. a faster local bus would
> seem to me to be an implementation detail.  It still sounds like a
> NUMA with three levels of memory access (CPU local, QBB local, remote
> QBB).   But all of the memory transparently visible in a program's
> address space.

You might think that but it wasn't. The fibre bus never actually worked
well. It was too slow mixed with PCI, with too much latency. It got
congested and bogged down under even moderate loads. DEC/Compaq's
engineers never solved that problem. These were the same people who
invented and perfected Memory Channel so if anyone could solve that
problem it was them. But they didn't and Galaxy never got past the
prototype.

-- 
Rich P.