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Hyper-Threading Technology is a form of simultaneous multithreading technology introduced by Intel, while the concept behind the technology has been patented by Sun Microsystems. Architecturally, a processor with Hyper-Threading Technology consists of two logical processors per core, each of which has its own processor architectural state.
The Intel Pentium 4 was the first modern desktop processor to implement simultaneous multithreading, starting from the 3.06 GHz model released in 2002, and since introduced into a number of their processors. Intel calls the functionality Hyper-Threading Technology, and provides a basic two-thread SMT engine
Whereas a normal superscalar processor issues multiple instructions from a single thread every CPU cycle, in simultaneous multithreading (SMT) a superscalar processor can issue instructions from multiple threads every CPU cycle. Recognizing that any single thread has a limited amount of instruction-level parallelism, this type of multithreading ...
Later versions introduced Hyper-Threading Technology (HTT). The first Pentium 4-branded processor to implement 64-bit was the Prescott (90 nm) (February 2004), but this feature was not enabled. Intel subsequently began selling 64-bit Pentium 4s using the "E0" revision of the Prescotts, being sold on the OEM market as the Pentium 4, model F.
[citation needed] Nehalem reimplements certain features of NetBurst, including the Hyper-Threading technology first introduced in the 3.06 GHz Northwood core, and L3 cache, first implemented on a consumer processor in the Gallatin core used in the Pentium 4 Extreme Edition.
All models support: MMX, SSE, SSE2, SSE3, Hyper-threading, Intel 64, XD bit (an NX bit implementation) Intel VT-x supported by: 6x2 e.g. Model 662 and 672; Enhanced Intel SpeedStep Technology (EIST) supported by: all except 620. Transistors: 169 million; Die size: 135 mm 2; Steppings: N0, R0
A barrel processor is a CPU that switches between threads of execution on every cycle. This CPU design technique is also known as "interleaved" or "fine-grained" temporal multithreading . Unlike simultaneous multithreading in modern superscalar architectures, it generally does not allow execution of multiple instructions in one cycle.
After joining the FreeBSD Security Team in 2004, Percival analyzed the behaviour of hyper-threading as then implemented on Intel's Pentium 4 CPUs.He discovered a security flaw that would allow a malicious thread to use a timing-based side-channel attack to steal secret data from another thread executing on the same processor core and sharing its cache.