8mm Tape drive interfacing

[Shigeki Misawa]

	Hi. I was wondering if anyone can steer me to some information
concerning 8mm tape drives and connecting them to unix systems. In
particular, I am interested in how data is written on the device and
how it is read back by the controller/computer. (I am not interested
in such details as the analog signals or the helical scan stuff, I
am really interested in such things as physical tape marks, end of
tape marks, end of file marks, end of record marks which may or
may not be used in 8mm tapes and whether things like this are under
operating system control or under control of the tape controller)
I am interested in this information because I will be writing tapes
from a VAX and/or a custom VMEbus multiprocessor and reading them back
on a UNIX box. I would have thought that the tape drive would act
as a system that would accept a byte stream from the computer. This
byte stream would fill up some buffer that would be flushed out to 
tape, at which point some sort of end of buffer mark would be
written by the tape controller to tape. Because of this, I would
expect that the computer/OS would insert record/file information
(including end of record, end of file, marks etc) into your file
and send that to the tape drive to be stored. When the tape is
read back, I would expect that the OS would filter this extra
information out of the stream and hand the information to the user
program that is reading the information.

This gets to the question of reading non Unix tapes on a Unix system.
I expect that the other OS's would insert incompatible information on
the tape. Is there a way to read bytes off such a tape with relatively
standard C calls?

	If anyone can steer me to any information that will give
me any information that may clear up any misconceptions on any of
the above topics, I would be greatful. Thanks in advance.


Shigeki Misawa UCB Physics Department Grad Student