Each of the three CPU cores on the Xbox 360 has two hardware threads; the hardware thread number selects a specific hardware thread on a specific core. Hardware threads 0 and 1 are the hardware threads on core 0; 2 and 3 are the hardware threads on core 1; and 4 and 5 are the hardware threads on core 2.
| Hardware Thread Number | Core |
|---|
| 0 or 1 | 0 |
| 2 or 3 | 1 |
| 4 or 5 | 2 |
Xbox 360 software threads are associated with, and run on, only a single hardware thread at a time. The hardware thread on which a thread runs (the thread's processor affinity) must be set to a single hardware thread, but can be subsequently changed by calling SetProcessorAffinity with a different hardware thread number. When a thread is created, it is initially assigned to the current hardware thread (that is, the hardware thread on which the current thread is running).
For Xbox 360 threads, you cannot clear the thread's processor affinity by passing an empty array as the cpus parameter. An Xbox 360 thread will always be associated with one hardware thread.
XNA Game Studio games should not use hardware threads 0 or 2, which are reserved for the XNA Framework. The following table identifies Xbox 360 hardware thread usage.
| Hardware Thread | Available |
|---|
| 0 | No, reserved for XNA Framework. |
| 1 | Yes |
| 2 | No, reserved for XNA Framework. |
| 3 | Yes |
| 4 | Yes |
| 5 | Yes |
To determine the number of hardware threads supported by the hardware, use System.Environment.ProcessorCount.
This method should not be used with threads created by the ThreadPool or Timer classes. It should only be called from the thread whose affinity is being changed.