A thread scheduled and run on a SPE. A program has one or more SPE threads. Each such thread has its own SPU local store (LS),.128 x 128-bit register file, program counter, and MFC Command Queues, and it can communicate with other execution units (or with effective-address memory through the MFC channel interface). The API call spe_context_run is a synchronous, blocking call from the perspective of the thread using it, that is, while an SPE program is executed, the associated SPE thread blocks and is usually put to "sleep" by the operating system.