A multiprocessing system including a multithreading microprocessor and multiprocessor operating system (OS) is disclosed. The microprocessor includes a first and a second plurality of thread contexts (TCs), each TC having a program counter and a general purpose register set for executing a thread. The microprocessor also includes a first and a second shared privileged resource, shared by the first and second respective plurality of TCs rather than being replicated for each of the respective first and second plurality of TCs, and privileged to be managed only by operating system-privileged threads rather than by user-privileged threads. The OS manages the first and second shared privileged resource and schedules execution of both the operating system-privileged threads and the user-privileged threads on the plurality of TCs.