Documented in Volume 1 of the UNIX Programmers Manual.
See also mt(1) and tar(1) for mag tape manipulation.
% dd if=/dev/rmt13 of=/va/you/diskfile bs=80 count=100
copy from physical drive 1 at 6250 bpi, and DO NOT rewind the
tape. The input and output block size are both 80 characters, and
only the first 100 80-character records will be copied. The results
are stored into the file /va/you/diskfile. This would be suitable for
80 column unblocked (blocked one) ascii data.
% dd if=/dev/rmt0 of=x ibs=800 cbs=80 conv=ascii,lcase
reads an EBCDIC tape blocked ten, 80-byte EBCDIC card images per
record. Convert it to an ascii file, fold all alphabetics to lower case,
and store it into file x.
NOTE the use of raw magtape (specified by rmt rather than mt).
if is input file name.
of is output file name.
count is number of records (blocks) to load
skip is number of records (blocks) to skip before starting copy
bs is input & output block size in bytes (superceding ibs and obs).
This is preferable when possible, as it saves buffer space.
ibs is input block size in bytes (default 512)
obs is output block size in bytes (default 512)
cbs is conversion buffer size
conv is the conversion(s) to be done
WARNING: Certain combinations of arguments to conv= are permitted.
However, the block or unblock option CANNOT be combined with ascii,
ebcdic or ibm. Invalid combinations "silently ignore" all but the
last mutually-exclusive keyword.
NOTE:
Units rmt0 and rmt1 are 1600 density and perform auto-rewind;
units rmt4 and rmt5 are 1600 density but DO NOT auto-rewind -
each set is equated to rmt0 and rmt1, respectively.
Units rmt8 and rmt9 are 6250 density and perform auto-rewind;
units rmt12 and rmt13 are 6250 density but DO NOT auto-rewind -
each set is equated to rmt0 and rmt1, respectively.
From: wcs@ho95b.UUCP (Bill Stewart)
Subject: Re: vax/unix to vax/vms
While ANSI-labelled tapes may be nice, I've found that the only
"machine-independent" tape format is EBCDIC non-labelled lrecl=80
blocksize=(whatever, but known and less than 4096).
Almost everything can read these, because they *have to*, and
most systems can write them.