Hyperthreading enables the Dual Core CPU to handle 4 threads at once (for a better usage of the pipeline).
超线程的双核心CPU可以处理4个线程在一次(一管道更好的使用)。
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When a query is executed, the work is evenly spilt among threads. But with both hyperthreading and virtualization, those threads are not running at a consistent speed.
The memory barrier performance of a single Intel P4 with hyperthreading (two processor cores on one die) is faster than with two P4s, and both have different performance characteristics than Sparc.