1、附录 A：英文资料 Progress in Computers The first stored program computers began to work around 1950. The one we built in Cambridge, the EDSAC was first used in the summer of 1949. These early experimental computers were built by people like myself with varying backgrounds. We all had extensive experience i
2、n electronic engineering and were confident that that experience would stand us in good stead. This proved true, although we had some new things to learn. The most important of these was that transients must be treated correctly； what would cause a harmless flash on the screen of a television set co
3、uld lead to a serious error in a computer. As far as computing circuits were concerned, we found ourselves with an embarass de richess. For example, we could use vacuum tube diodes for gates as we did in the EDSAC or pentodes with control signals on both grids, a system widely used elsewhere. This s
4、ort of choice persisted and the term families of logic came into use. Those who have worked in the computer field will remember TTL, ECL and CMOS. Of these, CMOS has now become dominant. In those early years, the IEE was still dominated by power engineering and we had to fight a number of major batt
5、les in order to get radio engineering along with the rapidly developing subject of electronics.dubbed in the IEE light current electrical engineering.properly recognised as an activity in its own right. I remember that we had some difficulty in organising a conference because the power engineers way
6、s of doing things were not our ways. A minor source of irritation was that all IEE published papers were expected to start with a lengthy statement of earlier practice, something difficult to do when there was no earlier practice Consolidation in the 1960s By the late 50s or early 1960s, the heroic
7、pioneering stage was over and the computer field was starting up in real earnest. The number of computers in the world had increased and they were much more reliable than the very early ones . To those years we can ascribe the first steps in high level languages and the first operating systems. Expe
8、rimental time-sharing was beginning, and ultimately computer graphics was to come along. Above all, transistors began to replace vacuum tubes. This change presented a formidable challenge to the engineers of the day. They had to forget what they knew about circuits and start again. It can only be sa
9、id that they measured up superbly well to the challenge and that the change could not have gone more smoothly. Soon it was found possible to put more than one transistor on the same bit of silicon, and this was the beginning of integrated circuits. As time went on, a sufficient level of integration
10、was reached for one chip to accommodate enough transistors for a small number of gates or flip flops. This led to a range of chips known as the 7400 series. The gates and flip flops were independent of one another and each had its own pins. They could be connected by off-chip wiring to make a comput
11、er or anything else. These chips made a new kind of computer possible. It was called a minicomputer. It was something less that a mainframe, but still very powerful, and much more affordable. Instead of having one expensive mainframe for the whole organisation, a business or a university was able to
12、 have a minicomputer for each major department. Before long minicomputers began to spread and become more powerful. The world was hungry for computing power and it had been very frustrating for industry not to be able to supply it on the scale required and at a reasonable cost. Minicomputers transfo
13、rmed the situation. The fall in the cost of computing did not start with the minicomputer； it had always been that way. This was what I meant when I referred in my abstract to inflation in the computer industry going the other way. As time goes on people get more for their money, not less. Research
14、in Computer Hardware. The time that I am describing was a wonderful one for research in computer hardware. The user of the 7400 series could work at the gate and flip-flop level and yet the overall level of integration was sufficient to give a degree of reliability far above that of discreet transis
15、tors. The researcher, in a university or elsewhere, could build any digital device that a fertile imagination could conjure up. In the Computer Laboratory we built the Cambridge CAP, a full-scale minicomputer with fancy capability logic. The 7400 series was still going strong in the mid 1970s and wa
16、s used for the Cambridge Ring, a pioneering wide-band local area network. Publication of the design study for the Ring came just before the announcement of the Ethernet. Until these two systems appeared, users had mostly been content with teletype-based local area networks. Rings need high reliabili
17、ty because, as the pulses go repeatedly round the ring, they must be continually amplified and regenerated. It was the high reliability provided by the 7400 series of chips that gave us the courage needed to embark on the project for the Cambridge Ring. The RISC Movement and Its Aftermath Early comp
18、uters had simple instruction sets. As time went on designers of commercially available machines added additional features which they thought would improve performance. Few comparative measurements were done and on the whole the choice of features depended upon the designers intuition. In 1980, the R
19、ISC movement that was to change all this broke on the world. The movement opened with a paper by Patterson and Ditzel entitled The Case for the Reduced Instructions Set Computer. Apart from leading to a striking acronym, this title conveys little of the insights into instruction set design which wen
20、t with the RISC movement, in particular the way it facilitated pipelining, a system whereby several instructions may be in different stages of execution within the processor at the same time. Pipelining was not new, but it was new for small computers The RISC movement benefited greatly from methods
21、which had recently become available for estimating the performance to be expected from a computer design without actually implementing it. I refer to the use of a powerful existing computer to simulate the new design. By the use of simulation, RISC advocates were able to predict with some confidence
22、 that a good RISC design would be able to out-perform the best conventional computers using the same circuit technology. This prediction was ultimately born out in practice. Simulation made rapid progress and soon came into universal use by computer designers. In consequence, computer design has bec
23、ome more of a science and less of an art. Today, designers expect to have a roomful of, computers available to do their simulations, not just one. They refer to such a roomful by the attractive name of computer farm. The x86 Instruction Set Little is now heard of pre-RISC instruction sets with one m
24、ajor exception, namely that of the Intel 8086 and its progeny, collectively referred to as x86. This has become 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 disap
25、points people like myself who come from the research wings.both academic and industrial.of the computer 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. hig
26、h 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 compatibility with previous usage when that can be attained. Nevertheless, things might have been different if Intels major attempt to pro
27、duce 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 e
28、asy 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； although it is not obvious, on the surface, a
29、modern x86 processor chip contains hidden within it a RISC-style processor with its own internal RISC coding. The incoming x86 code is, after suitable massaging, converted into this internal code and handed over to the RISC processor where the critical execution is performed. In this summing up of t
30、he RISC movement, I rely heavily on the latest edition of Hennessy and Pattersons books on computer design as my supporting authority； see in particular Computer Architecture, third edition, 2003, pp 146, 151-4, 157-8. The IA-64 instruction set. Some time ago, Intel and Hewlett-Packard introduced th
31、e IA-64 instruction set. This was primarily intended to meet a generally recognised need for a 64 bit address space. In this, it followed the lead of the designers of the MIPS R4000 and Alpha. However one would have thought that Intel would have stressed compatibility with the x86； the puzzle is that they did the exact opposite.
