Windows® via C/C++, Fifth Edition

Switching to Another Thread on a Hyper-Threaded CPU

Hyper-threading is a technology available on some Xeon, Pentium 4, and later CPUs. A hyper-threaded processor chip has multiple "logical" CPUs, and each can run a thread. Each thread has its own architectural state (set of registers), but all threads share main execution resources such as the CPU cache. When one thread is paused, the CPU automatically executes another thread; this happens without operating system intervention. A pause is a cache miss, branch misprediction, waiting for results of a previous instruction, and so on. Intel reports that hyper-threaded CPUs improve throughput somewhere between 10 percent to 30 percent, depending on the application and how it is using memory. For more ...