Lesson plan
Data Control Block
A Data Control Block (DCB) is a description of a dataset in IBM mainframe operating systems, such as OS/360, MVS, and z/OS. A DCB is coded in assembler programs using the DCB macro instruction (which expands into a large number of "define constant" instructions). High-level language programmers use library routines containing DCBs. A DCB is one of many control blocks used in these operating systems. A control block is a data area with a predefined structure, very similar to a C struct , but typically only related to system functions. A DCB may be compared to a FILE structure in C, but it is much more complex, offering many more options for access methods. The control block acted as the application programming interface between Logical IOCS and the application program and usually was defined within (and resided within) the application program. The addresses of I/O subroutines were resolved during a linkedit phase after compilation or else dynamically inserted at OPEN time. The equivalent control block for IBM DOS/360, DOS/VSE and z/VSE operating systems is a "DTF" (Define the file)
Article summary
A Data Control Block (DCB) is a description of a dataset in IBM mainframe operating systems, such as OS/360, MVS, and z/OS. A DCB is coded in assembler programs using the DCB macro instruction (which expands into a large number of "define constant" instructions). High-level language programmers use library routines containing DCBs. A DCB is one of many control blocks used in these operating systems. A control block is a data area with a predefined structure, very similar to a C struct , but typically only related to system functions. A DCB may be compared to a FILE structure in C, but it is much more complex, offering many more options for access methods. The control block acted as the application programming interface between Logical IOCS and the application program and usually was defined within (and resided within) the application program. The addresses of I/O subroutines were resolved during a linkedit phase after compilation or else dynamically inserted at OPEN time. The equivalent control block for IBM DOS/360, DOS/VSE and z/VSE operating systems is a "DTF" (Define the file)
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
Bibliography
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Key claims and bibliography are generated from the same tracked claims and sources as the article page.