IBM System/34 - Program Attributes - MRTs, SRTs, NRTs and NEPs

MRTs, SRTs, NRTs and NEPs

MRT = Multiple Requestor Terminal program. SSP could attach up to 7 terminals to a program at once. Any operator could start the program at their terminal, then other operators' terminals would be attached when they selected the same program. The maximum number of terminals to be serviced was controllable by the programmer.

SRT = Single Requestor Terminal program. Not a MRT.

NRT = No Requestor Terminal program. Started at a terminal, the NRT releases the requesting terminal and continues. This is similar to an MS-DOS TSR (Terminate and Stay Resident) program. By definition, any program that was EVOKEd or submitted to the JOBQ was a NRT.

NEP = Never Ending Program. This was typically an interactive MRT program that would wait after all terminals disconnected until some terminal reconnected, avoiding initiation overhead. This was commonly used to allow large programs to be implemented as a chain of small programs that would pass the terminals from one to another while remaining ready to continue processing for other terminals and/or subsequent transactions. NRT programs could also be NEPs if written to loop and wait for some condition indicating there was work to be done. NEP programs normally did not end until system shutdown, unless written to recognize some special terminate condition.