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'''Queued Telecommunications Access Method''' (QTAM) is an [[IBM System/360]] communications [[access method]] incorporating built-in [[Message queue|queuing]]. QTAM was an alternative to the lower level [[Basic Telecommunications Access Method]] (BTAM).

== History ==
QTAM was announced by [[IBM]] in 1965 as part of [[OS/360 and successors|OS/360]] and [[DOS/360 and successors|DOS/360]] aimed at inquiry and [[data collection]]. As announced it also supported [[remote job entry]] (RJE) applications, called ''job processing'', which was dropped by 1968. Originally QTAM supported the [[IBM 1030]] Data Collection System, [[IBM 1050]] Data Communications System, the [[IBM 1060]] Data Communications System, the [[IBM 2671]] Paper Tape Reader, AT&T 83B2 Selective Calling Stations, Western Union Plan 115A Outstations, and AT&T [[Teletype Model 33]] or 35 Teletypewriters. By 1968 terminal support had expanded to include the [[IBM 2260]] display complex, and the [[IBM 2740]] communications terminal.<ref name=MCP>{{cite manual|publisher=IBM|title=IBM System/360 Operating System Queued Telecommunications Access Method-Message Control Program|id=C30-2005-2|date=November 1968|url=http://bitsavers.org/pdf/ibm/360/os/qtam/C30-2005-2_QTAM_Message_Control_Program_Nov68.pdf}}</ref>{{rp|p.8}}

QTAM devices were attached to a System/360 multiplexor channel through an [[270x|IBM 2701 Data Adapter]] or [[270x|IBM 2702 Transmission Control]].<ref>{{cite manual|publisher=IBM|title=IBM Operating System/360 Telecommunications: Preliminary Specifications|id=C28-6553-2|date=December 1965|url=http://bitsavers.org/pdf/ibm/360/os/qtam/C28-6553-2_Telecommunications_Preliminary_Specifications_Dec65.pdf}}</ref> By 1968 support for the [[270x|IBM 2703 Transmission Control Unit]] had been added.<ref name=MCP />{{rp|p.8}}

QTAM was succeeded by [[Telecommunications Access Method|TCAM]] which provided roughly similar facilities, but was not supported under DOS.<ref>{{cite manual|publisher=IBM|title=OS Conversion Guide from QTAM or BTAM to TCAM|id=GC30-2026-0|date=April 1971|url=http://bitsavers.org/pdf/ibm/360/os/tcam/GC30-2026-0_OS_Conversion_Guide_From_QTAM_or_BTAM_to_TCAM_Apr71.pdf}}</ref>

== Structure ==
QTAM consists of a '''Message Control Program (MCP)''' and zero or more '''Message Processing Programs (MPP)'''. The MCP handles communications with the terminals, identifies input messages and starts MPPs to process them as required. This is similar in concept to the much later [[inetd|internet service daemon (inetd)]] in unix and other systems.

The '''MCP''' is assembled by the user installation from a set of [[Macro (computer science)|macros]] supplied by IBM. These macros define the lines and terminals comprising the system, the ''datasets'' required, and the procedures used to process received and transmitted messages.<ref name=MCP />{{rp|pp.31-93}}

The '''MPP'''s, incorporating logic to process the various messages, are supplied by the installation, and use standard OS/360 or DOS/360 data management macros <code>OPEN</code>, <code>CLOSE</code>, <code>GET</code>, and <code>PUT</code>. [[PL/I]] includes the <code>TRANSIENT</code> file declaration attribute to allow MPPs to be written in a high-level language.

== References ==
<references />

== Other sources ==
*{{cite manual
| author = IBM
| id = C30-2003-4
| title = IBM System/360 Operating System Queued Telecommunications Access Method-Message Processing Program Services
| url = http://bitsavers.org/pdf/ibm/360/os/qtam/GC30-2003-4_QTAM_Message_Processing_Program_Services_Jun71.pdf}}

*{{cite manual
| author = IBM
| id = C30-5003
| title = IBM System/360 Disk Operating System--QTAM Message Processing Program Services}}

*{{cite manual
| author = IBM
| id = C30-5004
| title = IBM System/360 Disk Operating System QTAM Message Control Program}}

{{DEFAULTSORT:Queued Teleprocessing Access Method}}
[[Category:IBM mainframe operating systems]]

{{Mainframe I/O access methods}}
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Queued Telecommunications Access Method - Revision history

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