V3/usr/man/man5/tap.5

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.he 'TAP (V)'6/12/72'TAP (V)'
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NAME		tap -- DEC/mag tape formats
.sp
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DESCRIPTION	The
DECtape command tap___ and
the magtape command mt__
dump and extract files to and
from their respective tape media.
The formats of these tapes are the same except
that magtapes have larger directories.
.sp
Block zero of the tape is not used.
It is available to contain a boot program to be
used in a stand-alone environment.
This has proved valuable for DEC diagnostic programs.
.sp
Blocks 1 through 24
for DECtape (1 through 146 for magtape)
contain a directory of the tape.
There are 192 (resp. 1168) entries in the directory;
8 entries per block;
64 bytes per entry.
Each entry has the following format:
.sp
.in +3
path name	32 bytes
.br
mode		1 byte
.br
uid		1 byte
.br
size		2 bytes
.br
time modified	4 bytes
.br
tape address	2 bytes
.br
unused		20 bytes
.br
check sum	2 bytes
.sp
.in -3
The path name entry is the path name of the
file when put on the tape.
If the pathname starts with a zero word,
the entry is empty.
It is at most 32 bytes long and ends in a null byte.
Mode, uid, size and time modified
are the same as described under i-nodes (see file system (V))
The tape address is the tape block number of the start of
the contents of the file.
Every file
starts on a block boundary.
The file occupies (size+511)/512 blocks
of continuous tape.
The checksum entry has a value such that
the sum of the 32 words of the directory entry is zero.
.sp
Blocks 25 (resp. 147) on are available for file storage.
.sp
A fake entry (see mt(I), tap(I))
has a size of zero.
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SEE ALSO	filesystem(V), mt(I), tap(I)