.TH TM 4 
.SH NAME
ht \- RH-11/TE-16 magtape interface
.SH DESCRIPTION
The files
.I "mt0, ..., mt15"
refer to the DEC RH/TM/TE-16 magtape.
Even numbered files are
800 bpi, and
odd numbered files are
1600bpi.
The files
.I "mt0, ... mt15"
unlike the files
.I "nmt0, ... nmt15,"
which are not.
When a file open for writing is closed, a double end-of-file is written.
.PP
A standard tape consists of a
series of 512 byte records terminated by an
end-of-file.
To the extent possible, the system makes
it possible, if inefficient, to treat
the tape like any other file.
Seeks have their usual meaning and it is possible
to read or write a byte at a time.
Writing in very small units is inadvisable,
however, because it tends to create monstrous record
gaps.
.PP
The
.I mt
files discussed above are useful
when it is desired to access the tape in a way
compatible with ordinary files.
When foreign tapes are to be dealt with, and especially
when long records are to be read or written, the
`raw' interface is appropriate.
The associated files are named
.I "rmt0, ..., rmt15"
and
.I "nrmt0, ..., nrmt15."
.PP
Each
.I read
or
.I write
call reads or writes the next record on the tape.
In the write case the record has the same length as the
buffer given.
During a read, the record size is passed
back as the number of bytes read, provided it is no greater
than the buffer size;
if the record is long, an error is indicated.
In raw tape I/O, the buffer must begin on a word boundary
and the count must be even.
Seeks are ignored.
A zero count is returned when a tape mark is read;
another read will fetch the first record of the
next tape file.
.PP
In raw mode, the 
.I ioctl
system call can be used to access device special functions.
This call takes the form:
.I "ioctrl(fdes, code, count)."
Codes are defined in
.I "<sys/mt.h>,"
and consist of:
.in +8
.ti -3
SKIPF: Skip blocks, forward direction
.ti -3
SKIPR: Skip blocks, reverse direction
.ti -3
WEOF: Write EOF
.ti -3
REW: Rewind
.ti -3
SKIPFF: Skip one or more EOF's (skip forward file)
.ti -3
SKIPRF: Skip EOF marks or to BOT, reverse direction
.in -8
The
.I count
argument must be positive, and specifies the number of times
the selected operation is to be repeated.
.SH FILES
/dev/mt?,
/dev/rmt?
.SH "SEE ALSO"
tp(1)
.SH BUGS
The magtape system is supposed to be able
to take 64 drives.
Such addressing has never been tried.
These bugs will be fixed when
we get more experience with this device.
.PP
The driver is limited to four transports.
.PP
If any non-data error is encountered, it refuses to do anything
more until closed.