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Data Control Block

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In IBM mainframe operating systems, such as OS/360, MVS, z/OS, a Data Control Block (DCB) is a description of a dataset in a program. A DCB is coded in Assembler programs using the DCB macro instruction (which expands in a large number of "define constant" instructions). High level language programmers use library routines containing DCBs.

A DCB is one of the many control blocks used in these operating systems. A control block is basically a data area with a predefined structure, very similar to a C struct, but typically only related to system's functions. A DCB may be compared to a FILE structure in C, but it is much more complex, offering much more options for various access methods.

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