双核，超线程的区别

http://www.richweb.com/cpu_info

单核超线程共享一个功能单元(可以理解为资源),可以同时执行两个线程,因此两个程序共同运行可能获得更好的性能.另一方面,如果你运行两个程序竞争同一个功能单元,则性能会下降.

双核处理器有两个功能单元,真正可以运行两个程序,而不必考虑竞争.

A hyperthreaded processor has the same number of function units as an older, non-hyperthreaded processor. It just has two execution contexts, so it can maybe achieve better function unit utilization by letting more than one program execute concurrently. On the other hand, if you're running two programs which compete for the same function units, there is no advantage at all to having both running "concurrently." When one is running, the other is necessarily waiting on the same function units.

A dual core processor literally has two times as many function units as a single-core processor, and can really run two programs concurrently, with no competition for function units.

A dual core processor is built so that both cores share the same level 2 cache. A dual processor (separate physical cpus) system differs in that each cpu will have its own level 2 cache. This may sound like an advantage, and in some situations it can be but in many cases new research and testing shows that the shared cache can be faster when the cpus are sharing the same or very similar tasks.

In general Hyperthreading is considered older technology and is no longer supported in newer cpus. Hyperthreading can provide a marginal (10%) for some server workloads like mysql, but dual core technology has essentially replaced hyperthreading in newer systems.

A dual core cpu running at 3.0Ghz should be faster then a dual cpu (separate core) system running at 3.0Ghz due to the ability to share the cache at higher bus speeds.


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