Basic telecommunications access method

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Basic Telecommunications Access Method (BTAM) was a low-level programming interface specified by IBM for use on the IBM System/360 for sending and receiving data through telecommunication lines. Later, IBM specified higher-level interfaces (QTAM, VTAM) and entire architectures (TSO, SNA).

BTAM requires the application program to handle almost every detail of the protocol. This is harder than using a higher-layer protocol, but it permits interfacing to non-standard devices in non-standard ways. At the time BTAM was introduced, there was little standardization anyway. Like most many of the System/360 programming interfaces, BTAM continued to be supported in later iterations of the system architecture. IBM finally withdrew support for BTAM in 2000.