This slide illustrates what a SYS/BIOS based system might look like. This not only shows a number of threads all executing together, but also a number of thread types. Because there is only one processor executing a single thread at any given time, the SYS/BIOS scheduler determines which thread runs at any given time. SYS/BIOS will prioritize hardware interrupts over other types of threads, and software interrupts over tasks. Each of these types can prioritize a thread to preempt the other.