VHDCI SCSI Progress

ham at subsys.enet.dec.com ham at subsys.enet.dec.com
Mon Mar 20 12:51:10 PST 1995


This note summarizes the progress made at the VHDCI working
group and SFF plenary in Newport Beach.  (VHDCI means very
high density cabled interconnect.)

Goals were set at the January meeting that a single
interface solution for wide SCSI for all the common PC's
(multiport on the same option slot) and the Type II PCMCIA
cards would be very attractive as a next generation external
SCSI standard.  The solutions would be based on the new
generation of connectors that use 0.8mm contact spacings.

At the March meeting in Newport Beach major progress was
made in acheiving the goals of multiport PC and single port
PCMCIA with the same interface solution.  Proposals from two
major suppliers showed 4 port wide SCSI on a single PC
option slot (for all common PC's) with the same interface
fitting nicely in a Type II PCMCIA card.  

Exactly the same cable assembly could be used for notebooks
and PC's. 

In addition, proposals were made to have the option of at
least two types of securing, jack screws and clips, on the
bulkhead side.  Slide releases were also discussed.  The
choice of securing method is left to the cable assembly
where most of the cost exists. 

Because of this major progress, it was decided to delay a
final selection until the May meeting.

Between the Newport Beach meeting and the Harrisburg meeting
in May two key activities will be occurring within and
between the connector/cable assembly suppliers:

     1.)  Verification of the dimensions and acheivability
          of 4 port wide SCSI on a single PC slot and a
          single port Type II PCMCIA card with the same
          interface

     2.)  Agreements to be compatible across suppliers for
          the mating interface and securing solutions

At least five major suppliers are actively working the
issues and have declared to be players.

It is very clear that any physical solution for wide SCSI
will be applicable to narrow SCSI by simply reducing the pin
count of the connectors.  On the other hand, if wide
solutions are used they will work very nicely for narrow as
well without changing anything physical.  The space and cost
gain for the narrow only solution is small with the VHDCI
implementations.  The wide solution gives a single interface
for all SCSI -- much simpler.

These new VHDCI solutions are also suitable as more user
friendly substitutes for the present external SCSI
connection schemes.

When combining the new VHDCI schemes with the new SCA
connectors being defined in SFF for use on devices we get a
truly new generation of SCSI interconnect that is well
suited for the design challenges in today's products.

At the moment the SFF descriptions are the closest thing
that exists to an industry standard for the latest SCSI
physical interfaces.  These are likely to migrate into the
formal ANSI process in the near future.  Because of the SFF
prework it appears unlikely that credible incompatible
challenges will emerge as the effort leaves SFF (quite
unlike previous SCSI connector ANSI processes).




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