Limitations of Intel Hyper-Threading Technology
Hyper-Threading, or HT, is a technology developed and used by Intel to improve performance on computer processors. It was a key feature with the release of the Pentium 4 processor in 2004, and is still used as of 2013, though not as widely. The technology has several limitations, which basically means that it doesn't always work as perfectly in practice as in theory.
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Concept
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Although computer processors are extremely quick, they are slowed down by the fact that they can only do one thing at a time. Many modern processors are split into separate cores -- such as a "dual core" or "quad core" processor -- but even then each core can only perform one task at a time, often leading to delays. Hyper-Threading involves the computer effectively splitting the queue of upcoming tasks for each core into two. This means it can more quickly and effectively assign specific tasks to specific cores on the processor and make the best possible use of the computer's resources. It reduces the likelihood that one core will be active with a backed-up line of tasks to perform, while another core lies unused.
Overstated Benefits
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The way Hyper-Threading works means the operating system acts as if each core was made up of two separate "virtual" processors. This has led to some misguided claims that these are literally real processors -- hence a double-core processor is billed as a quad-core processor -- or that Hyper-Threading doubles the power or speed of a processor. However, Hyper-Threading doesn't increase the physical resources of a computer at all, but simply uses them more efficiently. According to 2009 tests conducted by IXBT Labs, the actual increase in performance is notable, but varies depending on the task, with the highest result being a 28 percent speed increase.
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Compatibility
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To get maximum benefit from Hyper-Threading, the computer itself, the operating system and the specific applications must all take advantage of it. PCs running versions of Windows before XP cannot use Hyper-Threading; neither can some Linux-based systems. In addition, Hyper-Threading must be switched on in the BIOS settings of the computer, which are separate to the operating software. Processors with Hyper-Threading can work with any applications, but give more of a boost if the application is written with Hyper-Threading in mind.
Other Problems
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A 2006 report commissioned by rival chipmaker ARM claimed that Hyper-Threading used more energy than adding the equivalent number of real physical cores. The report noted that adding Hyper-Threading also increased the amount of cache-thrashing, a situation where the computer needs to repeatedly use its hard drive rather than its RAM, or memory, to store data temporarily, something that can slow down activity significantly.
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References
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