System Control Blocks

Offset
o (OJ 44
44 (2C) 1
45 (2D) • 5
Bytes and
Alignment
5Q (32) •• 2
52 (34; 4
56 (38) 2
58 (3A) •• 1
59 (3B) ••• 1
60 (3C) 2
62 (3E) •• 4
62 (3E)
64 (40)
66 (42) •• 2
FORMAT 4 -- VTOC DATA SET CONTROL BLOCK
Field Hex.
Name Dig. Field Description, Contents, Meaning
(padding 04
Bytes)
DS4IDFMT F4
DS4HPCHR
DS4DSREC
DS4HCCHH
DS4NOATK
DS4VTOCI
1 .••
1 ...
• 1 ••
.xxx •• xx
DS4NOEXT 01
DS4DEVSZ
Bytes 1-2
Bytes 3-4
DS4DEVTK
Hex 04 in each byte.
Format identifier,
Hex F4.
Highest address previQusly used for a format 1 DseB.
The address is in the format CCHHR.
Number of available format 0 DSCBs in the VTOC.
CCHH of next alternate track available.
Number of alternate tracks remaining.
VTOC indicators.
Either no format 5 DSCBs exist or they do not reflect
the true status of the volume.
Accurate format 5 and 6 DSCBs now exist and bit 0 has
been turned off. This volume may contain data sets
produced by IBM System/360 Disk Operating System; IBM
System/360 operating System access methods may not be
able to process these data sets.
A DADSM function has been prematurely terminated •
Possible VTOC errors exist.
(Reserved bits)
Hexadecimal constant '01' to indicate the VTOC is one
extent.
Reserved.
Device Constants (DS4DEVxx)
The following fields describe the device on which
this volume was mounted when the VTOC was created.
Device size.
Number of logical cylinders.
A logical cylinder is the smallest collection of two
or more tracks that can be processed by a set file
mask CCW (hex IF').
Number of tracks per logical cylinder.
Device track length.
Number of available bytes on a track exclusive of
home address and record zero.
Format 4 (VTOC) DSCB 185