9-track tape interfaces

Michael Sokolov msokolov at harrier.Uznet.NET
Tue Dec 8 17:19:34 AEST 1998


   Dear Tim,
   
   You write:
> Hmm - you said it has a 40-pin connector.
   
   Yes. A straight flat ribbon cable connects it to the bulkhead, which has
a female 37-lead D-sub connector on the outside.
   
> Any obvious buffers (or banks of buffers) near the external connector?
   
   I have just spent a couple of hours tracing the etches on this board,
and here is what I have found out. One side of the 40-pin connector is all
ground (well, that's pretty obvious). On other side we have the following.
4 pins are permanently connected to pull-up resistors, and one pin is
permanently connected to a pull-down resistor. The other 15 pins are
connected through jumpers so that the user can connect or disconnect them
on an individual basis. Some of these go to different outputs of a 74S241
(dual 4-bit 3-state buffer), some go to a 7437 (unfamiliar with this IC),
and some go to a missing IC.
   
   Both halves of the 74S241 are permanently enabled. All 8 outputs of this
half are connected to different pins on the connector. 7 of them are
connected in the obvious way, but one is also connected to a pull-up
resistor (purpose non-understood, since the 3-state buffer is always
enabled). The jumpers for all 8 are ON. Then there are 3 pins that go to
the 7437. Although 3 pins of the connector are used for this, 4 pins of the
7437 are used. Two of the connector pins go through simple jumpers, and
both are OFF. The third pin is connected to two different 7437 pins through
different jumpers. One of them is ON and the other is OFF. Finally, there
are 4 pins that connect to a missing IC. The jumpers for all 4 are OFF.
   
   Now, does this tell you anything? :-)
   
> What are the date codes on the chips?
   
   The most recent dates are mid-1988.
   
> [Explanation of the mess with host-side density control]
   
   OK, from now on I'll only use the front panel switch for density
selection. :-)
   
> other times they're used to put the drive into streaming
> vs non-streaming mode, other times it's used to change the speed on
> a streaming drive.
   
   Hmm, this is another big gap in my knowledge. What does streaming vs.
non-streaming mean?
   
> The QT13 will support either IDEN-style density select or CDC-style
> density select [...]
   
   How does it determine which one to use? Is there a switch on the board?
   
> Yep, the RC25 also used the LESI bus.  (LESI="Low End Storage
> Interconnect".)
   
   Hmm, so then KLESI can do disk MSCP as well as TMSCP, right? Can it do
both simultaneously or only one at a time?
   
> They all look similar, and have similar mechanics, but the 81's
> electronics can do 6250 BPI, something an 80's can't.
   
   But they are all different CDC Keystones, right? This means that my
Keystone may or may not support 6250 BPI, right? How can I tell?
   
> No, the Keystone and the Kennedy 9300 are not the same beast.  The
> Keystone is a cute little streaming tape drive, while the 9300 is
> a humongous [...]
   
   "Cute little"?!?! I mean, I'm still amazed how I was able to get it
inside my apartment without knocking a couple walls down first! It's
certainly huge compared to the REALLY cute little Cipher we had at CWRU. (I
really miss that Cipher, BTW. Not only is it much smaller, according to
what I have been able to glean from the docs, it's much easier to load
tapes into than the Keystone. But then of course if this Keystone does 6250
BPI I will be much more than happy with it.)
   
   But hey, if the Keystone is a cute little baby, poor CSRG fellows! I
think Kennedy 9300 was their primary machine, and I can just imagine what
it is like if the Keystone is "cute little". Does the 9300 do 6250 BPI?
   
> [...] vacuum-column 125IPS machine.
   
   Yet another gap in my knowledge. I remember seeing the term "vacuum
columns" in the BSD documentation and having no idea what are they. Could
you enlighten me?
   
> (I'm sure someone will
> now chime in about the days when Univac UniServo drives ruled the
> earth...)
   
   Just out of curiosity, what are they?
   
   Sincerely,
   Michael Sokolov
   Cellular phone: 216-217-2579
   ARPA Internet SMTP mail: msokolov at harrier.Uznet.NET


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