[net.periphs] SMD vs. MCSP, Unibus vs. Massbus vs. SBI: Does it matter?

roy@phri.UUCP (Roy Smith) (10/03/85)

	We're looking into buying a whole new I/O system for a used 11/780
we might be getting (it has old disks which we want to loose).  Is the type
of interface between the controller and the drives something I should worry
about?

	Other than MCSP-style coax cables being nicer to deal with than
SMD-style flat cables, are there any inherent advantages to MCSP over SMD
drives?  Assuming similar drive specs (seek time, RPM's, geometry), will
having one type of interface improve disk sub-system performance over the
other?  How far does the MCSP spec go?  Is it just the controller/drive
interface, or does it also imply UDA-50 emulation on the Unibus?

	Somewhat orthogonal to the above questions, how much difference
will I see between a Unibus disk and the same drive on a Massbus (or
directly on the CMI/SBI bus)?  I've read so many different bandwidth
figures for the various busses, I'm inclined to believe none of them.
Also, how much of a factor is underlying bus bandwidth going to be on
overall disk throughput?

	I realize these are broad questions, with answers depending on
the specifics of the particular situation.  What I'm really after is not so
much an answer to "Which disk is best for me?", but a guide to what factors
might go into the evaluation so I can come up with my own answer.
-- 
Roy Smith <allegra!phri!roy>
System Administrator, Public Health Research Institute
455 First Avenue, New York, NY 10016