moving 0.25" tapes between sun and 3b2 (was: Re: Writing HP cartridge tapes on a Sun 3)

[Randy_Davis]

In article <308 at pvab.UUCP> robert at pvab.UUCP (Robert Claeson) writes:
>In article <2871 at ttrdc.UUCP>, levy at ttrdc.UUCP (Daniel R. Levy) writes:
>
>> If you have the 60 MB SCSI drive (such as what the 3B2/600 has builtin, or
>> available as a SCSI accessory for other 3B machines), tapes written on
>> it are readable using /dev/[n]rst8 on a SUN with 0.25" cartridge tape drive
>> and vice versa.  The 23 MB 3B2/400 streaming drive isn't compatible with
>> anything on the SUN however.
>
>Oh, I tried it with a 3b2/400. Thought the /400 and the /600 were
>compatible.

  What do *you* mean by compatible???  Yes, they *ARE* compatible...  A program
compiled on a model 400 can be run on a model 600.  The floppy interface between
the 400 and 600 is identical (well, actually, the circuitry is better on the
600 - but they can both access the same format, etc...).  The option cards that
can be plugged into a model 400 can be plugged into the 600 (though not all 600
option cards can be put in a 400).
  In my observations, the model 600 is *backward compatible*, it may even be
advertised as such (I do not know - I have never seen an advertisement for one,
a big mistake on AT&T's part in my opinion).  This means that most everything
that runs on a 400 will run on a 600 (within reason - most exceptions are noted
as such).  This does *NOT* mean that everything that runs on a 600 will run on
a 400, or that you can trade hardware between the two without restrictions.
There is a large amount of common hardware (peripheral devices, circuit cards,
etc...) that are common between the two, but there are more non-common devices
than common ones.

  In this specific case, you are speaking of tape drives.  There are three
present types of quarter-inch cartridge (QIC) tape drives put into the 3B2 line
of computers.  The first, the 23 MB drive, is used only in certain model 400s,
though the interface card (the 195H circuit module) can be plugged into *any*
of the 3B2 computers, though I do not know why anyone would want to do so, with
the availability of the SCSI tape and subsystem.
  The second QIC tape drive is the 60 MB SCSI drive.  SCSI, meaning that it
interfaces to the SCSI bus, thus requiring a 3B2 SCSI Host Adpater (the 195W,
at present) to let the 3B2 talk to it.  The 60 MB drive is totally different
from the 23 Mb drive - different method of writing data on the tape, format
written "on the fly" with the data, inablility to make a file system because
it cannot seek, etc...  These limitations turn out to be trivial, as the tape
is almost always used as a backup device, for archival purposes instead of being
used as a filesystem.  Some models of the 400 come with the SCSI Host Adapter
and the 60 MB SCSI tape drive from the factory.
  The third type of QIC drive is the 120 MB SCSI drive.  It is very similar to
the 60 MB SCSI drive, and for that reason, just as different to the 23 MB drive
as the 60 MB is.  The 120 MB drive can even read the 60 MB tapes, though it will
only write in the 120 MB "format".

  The statement that you "thought the /400 and /600 were compatible" sounds
like a contradiction :-).  Dan said as much above, "the 23 MB 3B2/400
streaming drive isn't compatible with anything on the Sun however".  Does
Dan's statement make more sense now?  From Dan's statement I infer that the
Sun has something that speaks SCSI 60 MB QIC, but nothing that speaks the
23 MB....

Randy Davis                     		UUCP: ...(att!)ocrjd!randy
3B2 System Test Engineering                           ...(att!)occrsh!rjd
AT&T Network Systems, Oklahoma City Works
   All opinions and/or advice stated above are MY OWN, not those of AT&T.