9-track tape interfaces

[Michael Sokolov]

   Dear Tim,
   
   Your explanation of 9-track tape interfaces is extremely helpful!
Thanks! This area has always been a huge gap in my hardware knowledge.
   
   What I still don't understand is how do all these interfaces handle the
issue of recording density (800 BPI vs. 1600 BPI vs. 6250 BPI). You are
saying that the Pertec unformatted interface is very low-level. Do you mean
that it gives the controller the raw stream from the heads without trying
to separate data and clock bits? It is my understanding (please correct me
if I'm wrong) that the difference between 1600 and 6250 BPI is the data
encoding (PE vs. GCR) and that the actual magnetic density (flux
transitions per inch) is the same. If so, does this mean that a Pertec
unformatted transport can be made 1600 or 6250 BPI at the formatter's
discretion without the transport knowing or caring about the density? I
mean, is it like the ST-506/412 MFM vs. ST-506/412 RLL thing?
   
   And how does the Pertec formatted interface address this issue? In this
case the controller has to tell the transport what density it wants with
the transport being able to accept or deny the request depending on its
capabilities, right?
   
   You write:
> Yep, Pertec formatted.  The QT13 is nice because it'll emulate
> either MU: or MS:-type devices.
   
   This brings me to the following question. Assuming that the Pertec
formatted interface does carry explicit density control information, which
software interface would be a better choice in terms of density control,
TS-11 or TMSCP? It is my understanding that the original UNIBUS TS-11 is a
formatter for Pertec unformatted transports that supports 1600 BPI only,
right? If so, the TS-11 interface doesn't give the OS any control over the
density, does it? If so, what density does the QT13 choose in this mode?
And what about TMSCP? How much control does it give to the OS in terms of
density selection?
   
> Yep, a TS05 is a rebadged Cipher F880 (with some slightly-different
> firmware).
   
   And where does it stand density-wise? According to DEC, TS05 is a 1600
BPI only transport, and as far as I can remember, the Cipher at CWRU had
"1600 BPI" printed on the back somewhere. However, it had a switch on the
front panel labeled "HI DEN" or something like that. What the hell is this?
According to DEC docs, on TS05 this switch is labeled "ENTER" and the docs
call it "reserved".
   
> It probably had 4 50-pin edge connectors [...]
   
   Yes.
   
> [...] so that multiple drives could
> be chained on the same Pertec-formatted-bus.  (There are terminators at
> each end of the bus, much like SCSI.)  There's provisions for at least
> 4 formatters per bus, with each formatter potentially running multiple
> drives.
   
   Huh! I have never thought about it this way.
   
> (again, with slightly different firmware - for instance a DEC TU80
> controller
> will only work with TU80 drives or their CDC equivalent, the Keystone.)
   
   CDC Keystone is exactly what I have here. The interface coming out of
the (incredibly huge) cabinet is Pertec formatted. Does it have a Pertec
unformatted interface lurking inside or not? Which densities does it
support?
   
> TU80's and TS(V)05's are simple
> Pertec formatted interfaces.  Other times they convert to some other
> interface (Massbus, LESI, etc.) before the cables come out to the "real
> world".
   
   Hmm, the only DEC tape transport with LESI I know of is TU81+. Are there
any others? And what about that plus? Has there ever been a TU81 without
the plus? My manuals are at my main VAX farm from which I'm currently away,
but I remember the picture of the TU81+ in there looked similar to the
Keystone I have here. Since you say above that TU80 is Keystone in
disguise, does it mean that TU80, TU81, and TU81+ are all the same beast
with different interface converters tacked on?
   
   And what is LESI anyway? I have heard somewhere that the KLESI
controller can drive more than just a TU81+, so is LESI actually more than
just a tape interface?
   
   Oh, what about that leading edge strobe vs. trailing edge strobe? Your
vmsnet.pdp11 posting with the QT13 switch settings says that Kennedy 9300
uses trailing edge strobe while all others use leading edge strobe. Mine,
however, is set for trailing edge strobe, and it was connected to the
Keystone. Does this mean that the Keystone and Kennedy 9300 are the same
beast, or is it simply that the 9300 is not the only transport using
trailing edge strobe?
   
   Sincerely,
   Michael Sokolov
   Cellular phone: 216-217-2579
   ARPA Internet SMTP mail: msokolov at harrier.Uznet.NET


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