MEM11 update

Ian S. King isking at
Mon Feb 8 15:08:52 CST 2016

On Mon, Feb 8, 2016 at 1:04 PM, Guy Sotomayor <ggs at> wrote:

> > On Feb 8, 2016, at 12:43 PM, Noel Chiappa <jnc at>
> wrote:
> >
> >> From: Guy Sotomayor
> >
> >
> >> I also wanted to get folk's opinion on the need to actually produce an
> >> S[P]C form factor board. ... is it OK to have the MEM11 be outside of
> >> the 11/20 chassis and connect via BC11A (my replica) cables?
> >
> > Well, that's going to up the cost; for some people, that might be an
> issue.
> The reality (unfortunately) is that no matter what solution I take, it’s
> not
> going to be inexpensive.  The reality is that an SPC board will be more
> expensive because of the gold edge fingers.
> The other thing is that the boards will be fully assembled.  Except for
> some
> connectors and the UNIBUS transceivers, everything else is surface mount.
> I’m still crossing my fingers that I can keep within the 208 pin PQFP for
> the
> FPGA and not have to move into a BGA part.
> >
> > Also, I dunno if there are people out there with table-top 11/15's-20's
> (they
> > did exist BITD, I worked with a table-top one), but for them, an
> additional
> > box might be a hassle too.
> >
> >> That's assuming of course that the power requirements for the MEM11
> >> can be fulfilled by a single SPC slot. ... in the worst case, it may
> >> require splitting the MEM11 functionality across multiple boards.
> >
> > I guess I don't see the harm in making it two SPC (quad) boards? A flat
> cable
> > or two to connect across (I dunno how extensive the interconnect
> requirements
> > between the halves would be, and I have forgotten what the inter-slot
> > interconnect capabilities of an SPC backplane are - ISTR that it has some
> > bussing on the F section pins) would be easy and cheap.
> See above re: gold edge fingers.  I was originally thinking that if I do
> have to
> split the board up, that I’d make them completely independent.  But that
> has
> the issue of requiring 2x the number of UNIBUS transceiver parts (which are
> all but unobtainium as of now).  One of the things that drives up the
> power (and
> board area) are said transceivers (and level shifters, etc).  If I could
> come up
> with a reasonable alternative for the SPC version, that may work.  But
> that’s
> all in the future at the moment.
> TTFN - Guy
A thought: would a second quad board necessarily need transceivers?  I'm
thinking of the top-block connectors used in the PDP-8, and the top-plugged
ribbon cables for e.g., MicroVAX II CPU-to-memory connection.  You might
still want to grab power through a few fingers, but that's an
implementation detail.  -- Ian

Ian S. King, MSIS, MSCS, Ph.D. Candidate
The Information School <>
Dissertation: "Why the Conversation Mattered: Constructing a Sociotechnical
Narrative Through a Design Lens

Archivist, Voices From the Rwanda Tribunal <>
Value Sensitive Design Research Lab <>

University of Washington

There is an old Vulcan saying: "Only Nixon could go to China."

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