NDCBS parameter

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Number of file DCBs


Default value
Parameter type
Where set
On User 0's parameter line
Related products
Model 204 V2.1 or earlier


The number of file control areas for Model 204 database files

One file control area is needed for each dataset of each Model 204 database file currently open during the run: DCBs in z/OS and z/VM, and DTFs in z/VSE.

Normally, file control areas are released when all concurrent users have closed the file. The X'10' bit of FRCVOPT causes Model 204 to retain shared control of the file even when the file has been used by all users. If a file manager sets the X'10' bit on files, then NDCBS might need to be increased, because the file control area or areas used by the file are not released until the end of the job. If the file is reopened, no new file control areas are used.

The value of NDCBS is increased automatically for CCAGRP and CCASYS.

NDCBS can range from 1 to 32767 for z/OS and z/VM. For z/VSE, the maximum size you can specify depends on the label size of the operating system.