The DSC tape format.
	___________________


The blocks contain each a header of 8 words layed out as below. DSC
writes an initial type 40 block which contains the bootstrap and the
image name., followed by 1 or more blocks containing a description of
the index file, the information is the file sequence numbers which are
required to be generated into the new indexfile.

Files are dumped as a sequence of blocks,

	a type 2 block of 2048 + 16 bytes. 

	This contains general information from the file header, and
should be sufficient to name the file if DSC (at least in RSX11M v3)
didnt fill the filename and UIC fields with a constant. This block
type is also used by RMSRST. The only word used by RSTI is the
count of blocks used. The last 8 bytes are PUKCAB?? where the ?? is a
block checksum. 

	a type 4 block of 512 + 16 bytes

	This is a copy of the file header block from the indexfile.
DSC uses this to reconstruct a file on the output disk. It is not
present on the RMSBCK tapes.

	several type 1 blocks lengths 2048 + 16 bytes
	except the last which may be 512,1024,1536 or 2048 +16bytes

The file data blocks. The block # field in the 8 word header increments
by 4 between them. 
Intermediate type 4 records indicate the start of new file headers
in the inputfile.


HEADER
------

word 1	# of data bytes in block, not counting header. 512,1024,1536,2048
word 2	block type code. 1,2,4,40
word 3	block number in file being dumped
word 4	probably 2nd word of block #. always zero
word 5	File ID of file being dumped
word 6	File seq # of file being dumped
words 7,8 spare

The block # is zero for a type 2 or type 4 block.


The data follows immediately the 8 byte header