BTAM requires the application program or transaction processing system to handle almost every detail of the protocol.
It was not unusual for BTAM and later developed access methods (such as VTAM) to co-exist, supporting different devices simultaneously under the same transaction processing system.
The polling characters or telephone number used to identify each specific remote device on the line are coded.
The programmer can specify a buffer pool, a data structure used to hold messages transmitted to or from the terminals.
For read operations BTAM will automatically obtain one or more buffers from the pool and store the received message.
For a write operation the programmer needs to code REQBUF to obtain the number of buffers necessary to build the output message.
BTAM provides a large number of options for the READ and WRITE macros, depending on the line and terminal types and the current status.