Structure
QTAM consisted of a Message Control Program (MCP) and zero or more Message Processing Programs (MPP). The MCP handled communications with the terminals, identified input messages and started MPPs to process them as required. This is similar in concept to the much later internet service daemon (inetd) in unix and other systems.
The MCP was assembled by the user installation from a set of macros supplied by IBM. These macros defined the lines and terminals comprising the system, the datasets required, and the procedures used to process received and transmitted messages.
The MPPs, incorporating logic to process the various messages, were supplied by the installation, and used standard OS/360 data management macros OPEN, CLOSE, GET, and PUT. PL/I included the TRANSIENT file declaration attribute to allow MPPs to be written in a high-level language.
Read more about this topic: Queued Telecommunications Access Method
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