a multiprocessing system, including a multithreading microprocessor and a multiprocessor operating system (OS), is disclosed. The microprocessor includes a plurality of thread contexts (TCs) configured as an array, each having a program counter, a general purpose register set for executing a thread, and a register for storing an index of the respective TC within the array. The OS maintains a table of entries, each the entry for storing a CPU-unique value for a respective one of the TCs. The OS comprises a respective thread configured to execute on each of the respective TCs and to read the index from the register of the respective one of the TCs and to read the respective CPU-unique value for the respective one of the TCs using the index.