Ausam/doc/man/man5/dtp.5

.th DTP V 30/6/78
.sh NAME
dtp \*- magtape format
.sh DESCRIPTION
The command
.bd dtp
dumps files to and extracts files from magtape at 800 or 1600 bpi.
The tape consists of a series of 16384 byte records (32 disk blocks)
followed by a tape mark. This is the largest record which is a power of two
that can be written by DEC tape units at 800 bpi. Records of 32768 are possible
at 1600 bpi. The first record, and possibly subsequent records contain the tape
directory. Its format is as follows.
.s3
.in +5
.ta +6 +6 +18
.nf
struct dir_ent
{
	char	name[114];	/* file name */
	int	mode;		/* access modes */
	int	uid;	/* file owner */
	long	size;	/* size of the file in bytes */
	long	modtime;	/* last modification time */
	int	tapea;	/* tape address */
}
	dir_rec[128];
.fi
.in -5
.s3
.bd Name
is the pathname where the file was found,
.bd mode
are the permission modes of the file etc.
.bd Tapea
is the tape address of the file. It is a 512 byte block number which
is independent of the tape blocking. The first entry in the first tape block is
special. It contains information about the rest of the tape. Its format is
.s3
.in +5
.nf
struct tape_header
{
	int	nfiles;	/* number of files */
	long	dumptime;	/* tape creation time */
	int	ndirblks;	/* number of directory records */
	char	pad[120];	/* unused */
}
.in -5
.fi
.s3
There is always at least one record in the directory. The actual number can be
determined by reading the first one. After the directory there are sufficient
records to contain all the files that have been dumped. Files start on any
512 byte boundary in the record, and extend for (size+511)/512 continuous
blocks, which may extend over several tape records. Files are dumped in the
same order as they are in the directory. Thus the first file starts at the 
first data block. This allows tapes created by
.it dtp
to be distributed, as the dtp program can be the first file, which is easily
extracted by other means (eg. DD(I)).
.sh "SEE ALSO"
dtp(I), file system(V), ht(IV)