25 Oct
2012
25 Oct
'12
8:16 p.m.
On 10/25/2012 10:16 PM, David Riley wrote:
On Oct 25, 2012, at 10:02 PM, Dave McGuire wrote:
It's much worse for the KD32 (MicroVAX-I). Their memory is actually
on the Qbus, so not only do 32-bit transfers require two data cycles,
but Qbus is ALREADY a multiplexed bus! SSSSllllooooowwwww.
I love the KD32 anyway though. :) It was my first VAX, when I had
worshipped VAXen from afar for many years. And you know what? It
worked great. It was nowhere near as fast as my PDP-11/73, but the
additional functionality of VMS and a 32-bit CPU, and the GUI made life
so much nicer that I really didn't mind the performance hit. I still
have a MicroVAX-I...I should really get a working system disk for it and
get it running.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
On 10/25/2012 09:14 PM, Jon Elson wrote:
I was gonna say. The PMI interconnect for QBUS doesn't supply enough
address pins for VAX-sized memory, nor is it 32-bit, so MV boards have
their own ribbon cables as a side channel. Memory is NOT on the Q-bus, it has it's own
dedicated bus on
the C-D connector rows (how many slots are memory only in the
CD rows depends on the specific backplane.)
Actually the MicroVAX-II uses a PMI interconnect on a daisy-chained
ribbon cable across the tops of the memory and CPU boards, in addition
to the C-D interconnect.