Hyper-threading

Hyper-threading (officially Hyper-Threading Technology or HT Technology, abbreviated HTT or HT) is Intel's term for its simultaneous multithreading implementation first appearing in February 2002 on its Xeon server processors and in November 2002 on its Pentium 4 desktop CPUs. Later, Intel included this technology in Itanium, Atom, and Core 'i' Series CPUs, among others.

Intel's proprietary HT Technology is used to improve parallelization of computations (doing multiple tasks at once) performed on PC microprocessors. For each processor core that is physically present, the operating system addresses two virtual or logical cores, and shares the workload between them when possible. The main function of hyper-threading is to decrease the number of dependent instructions on the pipeline.

Hyper-threading requires not only that the operating system support multiple processors, but also that it be specifically optimized for HTT, and Intel recommends disabling HTT when using operating systems that have not been optimized for this chip feature.

Hyper-threading is a form of simultaneous multi-threading that takes advantage of super scalar architecture (multiple instructions operating on separate data in parallel). They appear to the OS as two processors, thus the OS can schedule two processes at once. In addition two or more processes can use the same resources. If one process fails then the resources can be readily re-allocated. The OS must support simultaneous multi-threading (SMT).