System trace provides an ongoing record of hardware events and software events that occurs during system initialization and operation. The system activates system tracing at initialization, which runs continuously, unless your installation has changed the IBM-supplied system tracing. After system initialization, you can use the TRACE operator command on a console with master authority to customize system tracing.
System trace writes trace data in system trace tables in the trace address space. System trace maintains a trace table for each processor.
Because system trace usually runs all the time, it is useful for problem determination. While system trace and the generalized trace facility (GTF) lists many of the same system events, system trace also lists events occurring during system initialization, before GTF tracing can be started. System trace also traces branches and cross-memory instructions, which GTF cannot do.