Simultaneous multithreading (SMT)

SMT is implemented on superscalar CPUs (implementing instruction-level parallelism), which include the x86 and ARM architectures. The defining characteristic of SMT is also indicated by its name, specifically, its ability to execute multiple threads in parallel, per core.

Generally, two threads per core is common, but some designs support up to eight concurrent threads per core. The main advantage of this is being able to share resources among threads, with an obvious disadvantage of conflicting needs by multiple threads, which has to be managed. Another advantage is that it makes the resulting CPU more energy efficient due to a lack of hardware resource duplication.

Intel's HT technology is essentially Intel's SMT implementation, providing a basic two thread SMT engine starting with some Pentium 4 CPUs in 2002.