Telecommunications Access Method (TCAM) is an

access method An access method is a function of a mainframe operating system that enables access to data on disk, tape or other external devices. Access methods were present in several mainframe operating systems since the late 1950s, under a variety of nam ...

, in IBM's

OS/360 and successors OS/360, officially known as IBM System/360 Operating System, is a discontinued batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964; it was influenced by the earlier IBSYS/IBJOB ...

computer operating systems on

IBM System/360 The IBM System/360 (S/360) is a family of mainframe computer systems that was announced by IBM on April 7, 1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover both commercial and scientific applica ...

and later, that provides access to terminals units within a teleprocessing network.

Features

TCAM provides similar functionality to

QTAM Queued Telecommunications Access Method (QTAM) is an IBM System/360 communications access method incorporating built-in queuing. QTAM was an alternative to the lower level Basic Telecommunications Access Method (BTAM). History QTAM was announc ...

, which it replaced. It was the access method for the initial version of

Time Sharing Option Time Sharing Option (TSO) is an interactive time-sharing environment for IBM mainframe operating systems, including OS/360 MVT, OS/VS2 (SVS), MVS, OS/390, and z/OS. Use In computing, time-sharing is a design technique that allows many peop ...

(TSO). With the advent of IBM's SNA, TCAM was eventually superseded by

VTAM Virtual Telecommunications Access Method (VTAM) is the IBM subsystem that implements Systems Network Architecture (SNA) for mainframe environments. VTAM provides an application programming interface (API) for communication applications, and c ...

. TCAM was said to have the following enhancements over QTAM: * Improved buffering, with more buffering options. * Improved organization of message queuing on disk including multiple volume support. * Back-up copies of messages maintained on disk. * Improved testing and debugging including off-line testing, improved debugging, online terminal testing, and logging. * Improved line handling for inquiry applications. * "Significantly increases speed and efficiency over QTAM." * Improved operator monitoring and control. * Binary Synchronous Support. * Checkpointing.

Structure

TCAM consists of a Message Control Program (MCP) and zero or more application programs. The MCP handles communications with the terminals, identifies input messages and starts application programs to process them as required. This is similar in concept to the much later internet service daemon (inetd) in unix and other systems. It is also similar to QTAM, where the application programs are called ''Message Processing Programs'' (MPP). The MCP is assembled by the user installation from a set of 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. The application programs, incorporating logic to process the various messages, are supplied by the installation, and use standard OS/360 data management macros OPEN and CLOSE, and either the ''Basic'' macros READ, WRITE, and CHECK, or the ''Queued'' macros GET and PUT. The use of SAM macros allows application programs to be tested in a

batch processing Computerized batch processing is a method of running software programs called jobs in batches automatically. While users are required to submit the jobs, no other interaction by the user is required to process the batch. Batches may automatically ...

environment.

Device support

TCAM initially supported *

Binary Synchronous Communications Binary Synchronous Communication (BSC or Bisync) is an IBM character-oriented, half-duplex link protocol, announced in 1967 after the introduction of System/360. It replaced the synchronous transmit-receive (STR) protocol used with second gene ...

(BSC) terminals * Start/stop terminals * 2260 terminals * message queuing in storage and on disk Support for 3270 terminals was soon added.

References

IBM mainframe operating systems {{mainframe-compu-stub