man/man4/tm.4

.pa 1
.he 'TM (IV)'6/12/72'TM (IV)'
.ti 0
NAME            tm -- TM-11/TU-10 magtape interface
.sp
.ti 0
DESCRIPTION     mt?\b\b\b___
is 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.
Reading less than 512 bytes
causes the rest of a record to be ignored.
Writing less than a record causes
null padding to 512 bytes.
When the magtape is closed
after writing,
an end-of-file is written.
.sp
Seek has no effect on the magtape.
The magtape can only be opened once at
any instant.
.sp
.ti 0
FILES           /dev/mt0        selected drive 0
.sp
.ti 0
SEE ALSO        mt(I)
.sp
.ti 0
BUGS            Seek
should work on the magtape.
Also, a provision of having the tape open for
reading and writing should exist.
A multi-file and multi-reel facility should
be incorporated.