In HSD, the current thread is initially set to the thread that was running on the processor when it stopped. If you are working with an unattached Code window, this shows details about the current thread.

When the current thread changes, for example when you stop the target with a different thread active, the Output view displays details of the new current thread. This includes the thread number in decimal and the thread name, if it is available.

Initially in RSD, the current thread is undefined and so RealView Debugger designates a thread at random to be the current thread.