A multiprocessing system, including a multithreading microprocessor and a multiprocessor operating system (OS), is disclosed. The microprocessor includes a plurality of thread contexts (TCs), each having a program counter and a general purpose register set for executing a thread. The OS includes a data structure having an entry for each of the plurality of TCs, each entry containing information describing capabilities of the corresponding one of the plurality of TCs. Each entry further comprises a TC identifier field for identifying a corresponding one of the plurality of TCs. The OS populates the TC identifier field for each of the entries with a unique identifier value.