Index Track Data Set Labels - IBM 3742 Reference Manual

Index Track Data Set Labels
Sectors 8 through 26 of the index track are used primarily
as data set labels. A data set label defines pertinent infor-
mation about a data set on the disk such as beginning of
extent (BOE), end of data (EOD), end of extent (EOE),
and the record length for the data set. For exact layout of
the data set label, see Figure 8.
Position by Position Representation of Data on the Index Track in Any One Sector of Sectors 8-26.
Field Name Position Purpose
Header 1 1-4 Label identifier for system appl ication; must be H D R 1. *
5 Reserved
Data set name 6-13 User name for data set
14-22 Reserved
Record length 23-27 Logical record length *
28 Reserved
Beginning of
29-33 Identifies the address of the first sector of the data set. Positions 29 and 30
extent (BOE) contain the track number, position 31 must be 0, positions 32 and 33
contain the sector number.*
34 Reserved
End of extent 35-39 Identifies the address of the last sector reserved for th is data set. *
(EOE)
40 Reserved
Bypass data set 41 The IBM 3747 data converter requires that this field contain a B or a blank.
If a B is present, the data set is ignored. If a blank is present, the data set is
processed. This coding allows the user to store programs and data on the
same disk.
Accessibility 42 This field must contain a blank in order for processing to take place.
Write protect 43
If this field contains a P, the disk can be read only. Otherwise this field must
be a blank, in which case both reading and writing are permitted.
* Indicates an entry required' by the 3740 system.
Figure 8 (Part 1 of 2). Data Set Label Layout
8