System Control Blocks

Data Set Control Blocks
The data set latel for a data set residing
on a direct access volume is called a data
set control block (OSCB). One or more OSCBs
are used to descrioe the data set. Each
OSCB is 140 bytes, consisting of a 44 byte
key and a 96 byte data portion.
The DSCBs describing all data sets on a
volume make up the volume table of contents
(VTOC) •
separate diagrams and descriptions are
presented for the following uses of DSCBs:
• Format 1 Identifier DSCB
• Format 2 Index DSCB
• Format 3 Extension DSCB
• Format 4 VTOC DSCB
• Format 5 Free Space DSCB
• Format 6 Shared Extent DSCB
In addition, there is a format 0 DSCB, the
free VTOC record. It has the same format as
other DSCBsi however, it contains all binary
zeros.
DSCB 165