Hyper-threading (officially termed Hyper-Threading Technology or HTT) is an Intel-proprietary technology used to improve parallelization of computations performed on PC microprocessors via simultaneous multithreading. It is an improvement on super-threading. It debuted in U.S. Patent 4,847,755 (Gordon Morrison, et. al) and can be seen in use on the Intel Xeon processors and Pentium 4 processors. The technology improves processor performance under certain workloads by providing useful work for execution units that would otherwise be idle, for example during a cache miss. A Pentium 4 with Hyper-Threading enabled is treated by the operating system as two processors instead of one.
Hyper-threading relies on support in the operating system as well as the CPU. Conventional multiprocessor support is not enough to take advantage of hyper-threading. For example, even though Windows 2000 supports multiple CPUs, Intel does not recommend that hyper-threading be enabled under that operating system.
Reference:
http://en.wikipedia.org/wiki/Hyper_threading
