IBM System/360 System Programmer's Guide

EMPTY=Ol DELETE=02 EMPTY and DELETE=03
Field 5: MaximuITr Generations Allowed (1 byte) -- contains the binary
count of the maximum number of generations allowed in the index at one
time as specified in the INDEX macro-instruction.
Field 6: Current Generation Count (2 bytes) -- contains the binary
count of the number of generations cataloged in the index.
The Volume Control Block Contents
A volume control block is composed of one or more volume-list blocks.
Each volume-list block contains an 8-byte key and a 256-byte data
portion. The data portion of the volume-list block can identify up to
20 volumes on which a data set is recorded. The format of the volume
list block is as follows:
Field 1: Number of volumes (2 tytes) -- the first volume-list block
contains the binary count of volumes on which the data set is stored;
the value of this field is reduced by 20 for each subsequent volume-list
block. If a data set is on 61 volumes, for example, it has four
volume-list blocks. The first field of each block contains 61,41,21,
and 1, respectively.
Field 2: Volume Identification (12 to 240 bytes) -- contains from 1 to
20 12-byte entries, each of which identifies a volume on which the data
set resides. Each entry contains a 4-byte device code, a 6-byte volume
serial number, and a 2-byte aata set sequence number. The data set
sequence number is zero for direct-access voluroes.
Field 3: Zero Field (10 bytes) -- contains binary zeros.
Field 4: Chain Address (3 bytes) -- contains the relative track address
of the next block of this volume control block, if additional blocks
exist. The address is in the form TTR. If this is the last block of
the volume control block, the field contains a binary zero. If this
field is not zero, this block must contain twenty 12-byte fields
identifying volumes of the data set.
Field 5: Zero Field (1 byte) -- contains binary zeros.
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IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English