V4/usr/man/man4/tm.4

Find at most related files.
including files from this version of Unix. 
.th TM IV 10/15/73
.sh NAME
tm \*- TM-11/TU-10 magtape interface
.sh DESCRIPTION
The files
.it "mt0, ..., mt7"
refer to the DEC TU10/TM11 magtape.
When opened for reading or writing,
the magtape is rewound.
A tape consists of a
series of 512 byte records terminated by an
end-of-file.
When the magtape is closed
after writing,
an end-of-file is written.
.s3
The magtape can only be opened once at
any instant.
.sh FILES
/dev/mt?
.sh "SEE ALSO"
tp(I)
.sh BUGS
If you hit the EOF mark
or get other non-data errors it refuses to do anything more
until closed.
There has to be some reasonable way to deal
with multi-file tapes.