9-track tape interfaces

[Tim Shoppa]

>1) I'd rather not spend a lot to get a SCSI interface.  I now have
>   Emulex TC02 and Dilog DQ130 Q-Bus controllers.  Is there
>   any way these controllers are going to enable 6250 BPI?

Sure - I use them at 6250 BPI all the time.  The controller
doesn't have to know what density the data is at - the formatter
takes care of that.  If you absoultely insist on the computer
being able to switch the drive between 1600 and 6250 BPI modes,
you won't be able to achieve this with a TC02 or DQ130 under 2.11BSD,
but this is purely a frill as you can always select the mode from
the drive's front panel.

One thing you do have to worry about is data rate.  Pertec
formatted interfaces on "fast" buffered modern drives may want to suck
or spew data at rates that are often too fast for a lowly TC02 or
DQ130's capability to push data over the Q-bus.  Most modern Pertec-
formatted drives will let you throttle the rate to something reasonable.
And some more modern Q-bus controllers - like the Dilog DQ152 - have
internal buffers for handling such cases without having to throttle
the drive itself.

>4) (Already asked in thread) Supposing I get the hardware to work
>   at 6250, will 2.11BSD handle it?

Absolutely.  I use a Fuji 2444 and a Storagetek 2925 with a TC02
and 2.11BSD all the time in 6250 BPI mode.  I had to throttle the
data rates on both, but that's not such a big deal.

On the other hand, my Storagetek 2920, which is pretty much a 2925
without the cache option, doesn't let me throttle the data rate
at 6250 mode because there is no effective buffer.  These don't
work with my TC02 on a Q-bus machine, but they do work with a TC13
on a Unibus 11/44 or with a DQ152 on a Q-bus -11.

Also keep in mind that some third-party controllers don't interact
well with the fast polling that the most recent Q-bus CPU's can
do.  For example, my TC02 won't work at all with
a loaned Mentec M100 (roughly comparable with a 11/93) that I have.  
I've never had this problem with 11/83's and slower CPU's.

-- 
 Tim Shoppa                        Email: shoppa at trailing-edge.com
 Trailing Edge Technology          WWW:   http://www.trailing-edge.com/
 7328 Bradley Blvd		   Voice: 301-767-5917
 Bethesda, MD, USA 20817           Fax:   301-767-5927

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