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发表于 2006-1-15 10:39:34
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Much of modern CPU design is dedicated to increasing the accuracy of the dispatcher system, and allowing it to keep the multiple units in use at all times. This has become increasingly important as the number of units has increased. While early superscalar CPUs would have two ALUs and a single FPU, a modern design like the PowerPC 970 include four ALUs and two FPUs, as well as two SIMD units. If the dispatcher is ineffective at keeping all of these units fed with instructions, the performance of the system as a whole will suffer greatly.
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RISC CPUs like these brought the superscalar concept to micro computers because the RISC design results in a simple core, allowing straightforward instruction dispatch and the inclusion of multiple functional units (such as ALUs) on a single CPU in the constrained design rules of the time. This was the reason that RISC designs were faster than CISC designs through the 1980s and into the 1990s, but as the chip manufacturing processes improved, even "complex" designs like the IA-32 were able to go superscalar.
Essentially all general purpose CPUs developed since about 1998 are superscalar.
http://en.wikipedia.org/wiki/Superscalar |
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发表于 2006-1-14 18:22:45
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