【正文】 ter design without actually implementing it. I refer to the use of a powerful existing puter to simulate the new design. By the use of simulation, RISC advocates were able to predict with some confidence that a good RISC design would be able to outperform the best conventional puters using the same circuit technology. This prediction was ultimately born out in practice. Simulation made rapid progress and soon came into universal use by puter designers. In consequence, puter design has bee more of a science and less of an art. Today, designers expect to have a roomful of, puters available to do their simulations, not just one. They refer to such a roomful by the attractive name of puter farm. The x86 Instruction Set Little is now heard of preRISC instruction sets with one major exception, namely that of the Intel 8086 and its progeny, collectively referred to as x86. This has bee the dominant instruction set and the RISC instruction sets that originally had a considerable measure of success are having to put up a hard fight for survival. This dominance of x86 disappoints people like myself who e from the research academic and the puter field. No doubt, business considerations have a lot to do with the survival of x86, but there are other reasons as well. However much we research oriented people would like to think otherwise. high level languages have not yet eliminated the use of machine code altogether. We need to keep reminding ourselves that there is much to be said for strict binary patibility with previous usage when that can be attained. Nevertheless, things might have been different if Intel’s major attempt to produce a good RISC chip had been more successful. I am referring to the i860 (not the i960, which was something different). In many ways the i860 was an excellent chip, but its software interface did not fit it to be used in a workstation. There is an interesting sting in the tail of this apparently easy triumph of the x86 instruction set. It proved impossible to match the steadily increasing speed of RISC processors by direct implementation of the x86 instruction set as had been done in the past. Instead, designers took a leaf out of the RISC book。A cyclist sets out on a circular cycling tour. Derive an equation giving the direction of the wind at any time. The singlechip puter At each shrinkage the number of chips was reduced and there were fewer wires going from one chip to another. This led to an additional increment in overall speed, since the transmission of signals from one chip to another takes a long time. Eventually, shrinkage proceeded to the point at which the whole processor except for the caches could be put on one chip. This enabled a workstation to be built that outperformed the fastest miniputer of the day, and the result was to kill the miniputer stone dead. As we all know, this had severe consequences for the puter industry and for the people working in it. From the above time the high density CMOS silicon chip was Cock of the Roost. Shrinkage went on until millions of transistors could be put on a single chip and the speed went up in proportion. Processor designers began to experiment with new architectural features designed to give extra speed. One very successful experiment concerned methods for predicting the way program branches would go. It was a surprise to me how successful this was. It led to a significant speeding up of program execution and other forms of prediction followed Equally surprising is what it has been found possible to put on a single chip puter by way of advanced features. For example, features that had been developed for the IBM Model giant puter at the top of the System 360 now to be found on microputers Murphy’s Law remained in a state of suspension. No longer did it make sense to build experimental puters out of chips with a small scale of integration, such as that provided by the 7400 series. People who wanted to do hardware research at the circuit level had no option but to design chips and seek for ways to get them made. For a time, this was possible, if not easy Unfortunately, there has since been a dramatic increase in the cost of maki ng chips, mainly because of the increased cost of making masks for lithography, a photographic process used in the manufacture of chips. It has, in consequence, again bee very difficult to finance the making of research chips, and this is a currently cause for some concern. The Semiconductor Road Map The extensive research and development work underlying the above advances has been made possible by a remarkable cooperative effort on the part of the international semiconductor industry. At one time US monopoly laws would probably have made it illegal for US panies to participate in such an effort. However about 1980 significant and far reaching changes took place in the laws. The concept of prepetitive research was introduced. Companies can now collaborate at the prepetitive stage and later go on to develop products of their own in the regular petitive manner. The agent by which the prepetitive research in the semiconductor industry is managed is known as the Semiconductor Industry Association (SIA). This has been active as a US organisation since 1992 and it became international in 1998. Membership is open to any organisation that can contribute to the research effort. Every two years SIA produces a new version of a document known as the International Technological Roadmap for Semiconductors (ITRS), with an update in the intermediate years. The first volume bearing the title ‘Roadmap’ was issued in 1994 but two reports, written in 1992 and distributed in 1993, are regarded as the true beginning of the series. Successive roadmaps aim at providing the best available industrial consensus on the way that the