TAP (V) 6/12/72 TAP (V)
NAME tap -- DEC/mag tape formats
DESCRIPTION The DECtape command tap and the magtape command
mt dump and extract files to and from their re-
spective tape media. The formats of these tapes
are the same except that magtapes have larger di-
rectories.
Block zero of the tape is not used. It is avail-
able to contain a boot program to be used in a
stand-alone environment. This has proved valu-
able for DEC diagnostic programs.
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 direc-
tory; 8 entries per block; 64 bytes per entry.
Each entry has the following format:
path name 32 bytes
mode 1 byte
uid 1 byte
size 2 bytes
time modified 4 bytes
tape address 2 bytes
unused 20 bytes
check sum 2 bytes
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.
Blocks 25 (resp. 147) on are available for file
storage.
A fake entry (see mt(I), tap(I)) has a size of
zero.
SEE ALSO filesystem(V), mt(I), tap(I)