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Hyperthreading, also known as Hyper-Threading Technology (HTT) or Simultaneous Multi-Threading (SMT), is Intel's proprietary implementation of simultaneous multi-threading for microprocessors. It allows a single physical CPU core to act as two logical cores for the operating system and applications. This is achieved by duplicating certain parts of the processor, such as the architectural state, but not the full execution units. When one logical core is stalled, for example, waiting for data from memory, the other logical core can utilize the available execution units, thereby increasing overall processor utilization and performance.

Hyperthreading does not double the processing power of a core, as it still shares the same physical execution resources. However, it can significantly improve performance in multi-threaded applications or when running multiple applications concurrently by keeping the processor's execution units busier. The effectiveness of Hyperthreading can vary depending on the workload; it is most beneficial when tasks are frequently stalled waiting for resources, allowing the other logical core to make progress. In heavily CPU-bound tasks that utilize all execution units continuously, the performance gain may be minimal or even negligible.

The technology was first introduced by Intel in 2002 with the Pentium 4 processor. While initially met with mixed reactions, it has become a standard feature in many modern Intel processors, contributing to their ability to handle multitasking more efficiently. Other processor architectures, such as AMD's processors, also implement similar SMT technologies.