Data set (IBM mainframe): Difference between revisions

Revision as of 02:15, 11 October 2021

Revision as of 13:20, 11 October 2021

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|url=https://www.ibm.com/support/knowledgecenter/zosbasics/com.ibm.zos.zconcepts/zconcepts_172.htm

|title=What is a catalog?

|quote=Cataloging of data sets on magnetic tape ...}}</ref> however unit record devices, such as punch card readers, card punchpunches, line printers and linepage printers can provide input/output (I/O) for a data set (file).<ref>{{cite web|url=http://publib.boulder.ibm.com/infocenter/zvm/v5r4/index.jsp?topic=/com.ibm.zvm.v54.hcpa7/hcse7b3050.htm|title=IBM Knowledge Center - Home of IBM product documentation|website=publib.boulder.ibm.com}}</ref>

Data sets are not unstructured streams of [[byte]]s, but rather are organized in various logical record<ref>{{cite web

|url=https://www.ibm.com/support/knowledgecenter/zosbasics/com.ibm.zos.zconcepts/zconc_datasetintro.htm

|title=What is a data set? |quote=data set .. a file that contains one or more records.}}</ref> and block structures determined by the <code>DSORG</code> (data set organization), <code>RECFM</code> (record format), and other parameters. These parameters are specified at the time of the data set allocation (creation), for example with [[Job Control Language]] <code>DD</code> statements. Within a running program they are stored in the [[Data Control Block]] (DCB) or Access Control Block (ACB), which is aare data structurestructures used to access data sets, for example using [[access method]]s.

Records in a data set may be fixed, variable, or “undefined” length.<ref>{{cite web

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==Data set organization==

For OS/360, the DCB's <code>DSORG</code> parameter specifies how the data set is organized. It may be<ref>{{cite physically sequential ("PS"), indexed sequential ("IS"), partitioned ("PO"), or Direct Access ("DA"). Data sets on tape may only be DSORG=PS. The choice of organization depends on how the data is to be accessed, and in particular, how it is to be updated.manual

| title = IBM System/3S0 Operating System: Job Control Language Reference - OS Release 21.7

| id = GC28-6704-4

| section = Section IV: The DD Statement -- DCB Parameter

| section-url = http://bitsavers.org/pdf/ibm/360/os/R21.7_Apr73/GC28-6704-4_OS_JCL_Aug76.pdf#page=138

| pages = 138-139

| url = http://bitsavers.org/pdf/ibm/360/os/R21.7_Apr73/GC28-6704-4_OS_JCL_Aug76.pdf

| work = Systems Reference Library

| publisher = IBM

}}

</ref>

;CQ

:[[Queued Telecommunications Access Method]] (QTAM) in Message Control Program (MCP)

;CX

:Communications line group

;DA

:[[Basic Direct Access Method]] (BDAM)

;GS

:Graphics device for Graphics Access Method(GAM)

;IS

:[[Indexed Sequential Access Method]] (ISAM)

;MQ

:QTAM message queue in application

;PO

:Partitioned

;PS

:Physical Sequential

among others.

Data sets on tape may only be DSORG=PS. The choice of organization depends on how the data is to be accessed, and in particular, how it is to be updated.

Programmers utilize various [[access method]]s (such as [[Queued Sequential Access Method|QSAM]] or [[VSAM]]) in programs for reading and writing data sets. Access method depends on the given data set organization.