"Multi tasking" was implemented by PL/I F, the Optimizer and the newer AIX and Z/OS compilers. It comprised the data types codice_104 and codice_105, the codice_106 on the codice_107 (Fork), the codice_108 (Join), the codice_109, codice_110s on the record I/O statements and the codice_111 statement to unlock locked records on codice_112 files. Event data identify a particular event and indicate whether it is complete ('1'B) or incomplete ('0'B): task data items identify a particular task (or process) and indicate its priority relative to other tasks.