TP(V)                        9/10/73                        TP(V)


     tp - DEC/mag tape formats


     The command tp dumps and extracts files to and  DECtape  and

     magtape.   The  formats  of  these tapes are the same except

     that magtapes have larger directories.

     Block zero  contains  a  copy  of  a  stand-alone  bootstrap

     program.  See boot procedures (VIII).

     Blocks 1 through 24 for DECtape (1 through 62  for  magtape)

     contain  a directory of the tape.  There are 192 (resp. 496)

     entries in the directory; 8 entries per block; 64 bytes  per

     entry.  Each entry has the following format:

         path name            32 bytes

         mode                 2 bytes

         uid                  1 byte

         gid                  1 byte

         unused               1 byte

         size                 3 bytes

         time modified        4 bytes

         tape address         2 bytes

         unused               16 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, gid, size and time modified are the

     same as described under i-nodes (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. 63) on are available for file storage.

     A fake entry (see tp(I)) has a size of zero.


     file system(V), tp(I)