Telecommunications Access Method

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Telecommunications Access Method (TCAM) is an access method, in IBM's OS/360 and successors computer operating systems on IBM System/360 and later, that provides access to terminals units within a teleprocessing network.[1]


TCAM provided similar functionality to QTAM, which it replaced. It was the access method for the initial version of Time Sharing Option (TSO).

TCAM was said to have the following enhancements over QTAM:[2]

  • 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.

Device support[edit]

TCAM initially supported

Support for 3270 terminals was soon added.


  1. ^ Burnie Blakeley, Harry Harris, and Rhys Lewis (1995). Messaging and Queuing Using the Mqi: Concepts & Analysis, Design & Development. McGraw-Hill. p. 9. ISBN 0-07-005730-3. 
  2. ^ IBM Corporation (1973). OS TCAM Concepts and Facilities (PDF).