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Software and Ur~ortlodox Architectures: Where Are We Headed? MICHAEL L. DERTOUZOS SOFTWARE Can you construct a 10-mile-long wooden bridge? The answer is not very relevant. What is relevant is that if this question is posed to 100 civil engineers, they will answer either yes or no fairly consistently. Now for a question at the cutting edge of computer science research: Can you mimic an airline office by a computer program so that when someone types in a query that would normally be placed by telephone "Do they serve meals on the flight from here to Atlanta?" or "What time does the flight leave?"the automated system responds on that person's terminal with the kind of answer that would be given over the telephone? Can you construct a system that will answer 80 percent of these questions correctly? I have asked this question of many people working on the leading edge of computer science research, and their typical answer is "Give us $2 million and about two years." While I have not carried the experiment further? I know that if I were to pursue it, in two years the answer would be either "Here it is, and it's answering correctly 75 percent of the queries" or "Give us another $2 million and another two years." The point here is that with the exception of com- puter science theory and compiler design, there is very little science in this field, which in my opinion is still largely experimental in nature. The cutting edge of computer science is very much like alchemy in the old days mix two liquids and if there is an explosion take notes. Leav- ing some room for poetic license, that is the approximate situation with 27

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28 COMPUTERS OF THE FUTURE most of our advanced programs and with many of our avant-garde hard- ware architectures, as will be seen. As a result of this absence of "laws" in the world of software, the programmer is the lawmaker. That, in a nutshell, is the power and attraction of programming: to set good laws and to build complex struc- tures based on these laws. For this reason programmers are extremely reluctant to "buy" each other's laws; each one wants to be the lawmaker. That is also why young people become millionaires by starting pro- gramming companies their fresh minds are not burdened by the excess baggage of experience, and they can accordingly thrive in creating and adhering to new laws. What can educators really teach to a young aspiring programmer? Unfortunately, very little. Educators can issue generalities and plati- tudes, such as, "Design your programs in nice modules, isolate them, make each module neat and tidy and describe its inputs and outputs." This is an exaggeration, of course, but there is very little about pro- gramming that can be taught explicitly. Educators do ask young pro- grammers to read other people's programs and to apprentice by watching experienced programmers at work. The effectiveness of these ap- proaches again suggests that the similarity to alchemy or even to sculp- ture may not be too farfetched. Traditional software generation cannot be substantially improved with the techniques that are in hand today or that have been developed over the last 20 years. While the hardware cost/performance improves at the rate of roughly one decade per decade, the corresponding software- improvement is by comparison insignificant: During the last 10 years software productivity measured as lines of program produced per pro- grammer per year has increased by about 50 percent. Are there any prospects for improving software productivity? I will discuss a few. Structured programming is a technique that is most ef- fective if one deals with very small programs, often three or four lines long. I am reminded of the pioneer of structured programming, the famous Professor Dijkstra, who spent an hour explaining to a large audience at MIT how a three-line program could be verified. One of our students asked: "But how would you apply this to a chess-playing program?" And Dijkstra, in his inimitable style, said: "One should never write such complicated programs." More seriously, I believe that struc- tured programming has been helpful, but we seem to have exhausted its benefits. Automatic programming was a technique attempted, without much success, during the last 15 years. The intent was to describe something like an inventory control process at a very high level and then to use a

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SOFTWARE AND UNORTHODOX ARCHITECTURES 29 gigantic compiler to generate the high-level programs (e.g., in COBOL) that one would normally write for inventory control. This approach did not work well for reasons of complexity and variance among different users' needs. Functional programming is a recent approach that tries to build pro- grams in the form of mathematical functions that have inputs and outputs and, significantly, no side effects. Different functional programs can be combined in the same way that complex mathematical functions can be composed out of simpler ones. It is too early to predict how well this approach will work, and it is difficult at this time to bend into the functional mold traditional programs used, for example, in data base management, where side effects are the governing mechanisms. There is currently great hope that expert systems will be useful in programming; this would mean that an "expert assistant"a pro- gram- would help us program more effectively. Unfortunately it is too early for a meaningful assessment of this prospect. My own overall assessment about the future success of programming productivity improvements is rather bleak. But let me ask a provocative question: Why do we need programming? To go back 20 to 25 yearsin the days of batch computing people programmed because there was a very expensive resource called the computer that cost several million dollars to acquire. They waited in line for hours if not days to get their cards processed into results, only to modify their programs against that "last bug" so that they could stand again in the waiting line. Later, in the late 1960s, time-sharing came along. At the beginning at least, the reasons for developing and using time-shared systems were the same. The same very expensive resource could now be shared by many people in round-robin fashion so that each user did not, it was hoped, notice the delay. Soon thereafter, time-sharing pioneers changed their position and said that cost-sharing was no longer a valid reason for these systems. Instead, attention was focused on the utility aspects and the services offered by those systems. And that, indeed, turned out to be one of the great truths about the ultimate usefulness of time-shared systems. Now, with computer costs dropping dramatically, the personal ma- chine that I have next to my desk costs $5,000 and does more than the $2.5-million time-shared machine that we had in our lab 20 years ago. To the extent that this is now the case, why is programming needed anymore? Certainly not for cost-sharing. It is needed for application flexibility, i.e., to carry out different applications on the same piece of equipment.

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30 COMPUTERS OF THE FUTURE Let me now ask a second provocative question. We have said that while the hardware is improving at the rate of 30 percent per year, software productivity is essentially standing stillhence we are con- fronted with a "great software problem." The question is simply this: Is there really a software problem? In my opinion the answer is no for this reason: Because software involves paper and pencil and not the traditionally difficult tasks of putting hardware together into complex physical systems, there is a tendency to assume that software ought to be easier. This is even reflected in the legal differentiation made between software and hardware: one is patentable while the other is "copyright- able." Compare, however, the design of the airline office program mentioned earlier with the design of a complex physical system like a jumbo jet and not the routine twentieth design of a jumbo jet, but the original design of such an airplane. This comparison deals with two objects of roughly the same complexity in terms of the elements that they contain. And while people might laugh about the airline office program taking several years to design, they would readily agree that such a long design time would be reasonable and proper in the case of the jet plane. In my experience there is neither precedent nor prospect for achieving dramatic economies in the design of complex systems, especially in the case of first designs, which are typical of novel software systems. In these cases creativity plays an important role since one is trying to break new ground. There is no reason to believe that in the field of program- ming this endeavor ought to be easier than in any other discipline that depends heavily on creative design. Let me close this section on software prospects with some good news. There is ample precedent for economizing through the mass production process, e.g., by spreading the very expensive cost of designing a com- plex product to the people who buy it. Accordingly, I would suggest that one of the biggest forces before future software developments is the transition of the software devel- opment process from the artisan to the mass production era. In partic- ular, two significant categories of products can be expected to emerge in the next decade. The first category can be called hidden computers, because it deals with "appliances" performing a useful function. These products will not be thought of as computers any more than cars are thought of as col- lections of carburetors and other components, or refrigerators'as electric motors. Each hidden computer is especially programmed for one ap- plication, not changing its program, and providing immediate utility to its user. Examples include the drugstore machine, the personal memo

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SOF7~VLARE AND UNORTHODOX ARCHITECTURES 31 pad, the automobile safety package, the automobile convenience pack- age, the fuel control package, the automobile maintenance package, and so on. The second emerging category of software products is mass-manu- factured applications in the form of diskettes, which in time will become more powerful and more useful. In both categories the large costs in- curred in the design and production of these items become very small when spread to hundreds of thousands or even millions of users. Finally, I do expect that more intelligent programs will make life easier for all of us. When I am told that a certain program or machine has a friendly user interface I get a bit worried, because I find that I need 40 or 50 hours to become truly acquainted with a new machine, and I am a computer professional. Such a relationship may be friendly compared with a life-threatening situation, but it is not a relationship we should have with something next to our desk. I believe that the only way to achieve true friendliness with computers is by increasing the intelligence of the programs that they contain. Only then will machines begin to understand what we are trying to do in the same sense that friends understand what we mean when we communicate with them. FORTHCOMING SYSTEM ARCHITECTURES The dominant theme in forthcoming machine architectures will be the myria-processor system. In Greek, myria means 10,000. That number may be close to what will be used in practice, at least in the next 15 to 20 years. Look, then, for future computer systems that use hundreds or thousands of processors. Myria-processors will be used in two areas. The first involves the so- called geographically distributed systems. This architecture is evolving because people who generate and collect data are geographically dis- tributed. Moreover, organizations have geographically distributed of- fices and personnel who need to communicate with one another. And, of course, there is a great techno-economic opportunity along with these needs in that people can now afford to buy computers and the com- munications products and services that interconnect them. The second area of myria-processor revolution involves tightly coupled multiprocessor systems. Here I envision again hundreds or thousands of processors in one very big box, devoted to one task, for example, recognizing the face of one human being among a few thousand or trying to comprehend human speech. As in the case of distributed systems, a sizable techno-economic opportunity is driving us in this direction, with

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32 COMPUTERS OF THE FUTURE the very low cost of individual processors making such large systems affordable. Geographically Distributed Systems Consider 1,000 autonomous machines that are geographically distrib- uted autonomous because each machine can support the desires of its owner in editing text, handling messages, and running application pro- grams, all independently of what other people are doing on their com- puters. In addition to this autonomy, however, each computer must cooperate with the other computers in the system, whether they are 1,000 miles away or upstairs, in order to make possible common appli- cations, e.g., planning, putting together a manual, or trying to figure out why there was a power failure in New York City. The electronic interconnections among computers, which are a com- bination of local-area networks and long-distance terrestrial or satellite networks, are fairly straightforward at the hardware level and present no substantive long-range problems. Large companies that have begun to establish networks of distributed systems are approaching these sys- tems from an era in which dumb terminals became progressively more intelligent in the presence of a central powerful program that controls everything in the system. It is now becoming clear that these intercon- nected machines need to be autonomous and that there can be no central "executive." The reason for this decentralization lies in the desire to establish arbitrarily large systems: A centrally directed system has an upper size limit of perhaps 50 to 100 nodes for the same reason that an individual can only converse simultaneously with a small, limited number of people. Achieving truly decentralized systems will require the de- velopment of some form of common currency or, if you wish, simple Englishfor computers so that these machines can "understand" each other for the purpose of common applications. This requirement is at least philosophically analogous to the communication means in humans tribes: Each individual is autonomous, yet the aggregate can embark on common activities because they can understand one another. Ulti- mately these computer tribes will form an "information marketplace," i.e., a free market dedicated to the purchase and sale of information and informational labor. Now let me pose a challenge to computer professionals: Can you construct a 1,000-computer distributed system that at minimum has the behavior and performance of a traditional, centralized, time-shared sys- tem that services perhaps 50 users in round-robin fashion? The choice of the number 1,000 is of course arbitrary. If this goal can be achieved

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SOFTWARE AND UNORTHODOX ARCHITECTURES 33 for 1,000 machines, I would immediately ask if it can be done for 10,000 or even a million computers. In short, is there a scalable system archi- tecture that permits the kinds of services and the sharing of data that transpire in time-shared communities? I have posed this challenge in terms of time-shared systems because there is experience in that area, and it is known that if this behavior and performance can be extended to arbitrarily many users the result will have proven utility. This question has not yet been answered. It seems, however, that it must be answered one way or another before distributed computer sys- tems become truly useful. Let us look, for comparison purposes, at an existing network called the ARPANET, which spans several hundred computers from Hawaii to West Germany. In principle and in practice it is possible to log into any computer on this network and to use that computer from a remote location. Yet, hardly anyone does this. Instead, people use this network as a very sophisticated message-exchange medium, which has proven its utility for that purpose. The reason that remote use of computers does not take place is that dialing into another computer generally means being confronted with an entirely different system that speaks its own language and has its own conventions, which are either unknown to the person dialing in or are costly to learn. Hence, except for the great young hackers who enjoy exploring remote computers, most people have very little use for such an unknown and remote resource. Regardless of the success of devising effective decentralized and dis- tributed computer systems, individual computer "nodes" are likely to continue their rapid evolution. The dominant trend that I see is toward more powerful personal computation. In this regard people often ask if they really need in their personal computers more memory than 128,000 characters, half a million characters, or at most 1 million characters (1 megabyte). The answer is an easy yes. If we focus on greater program intelligence, which is the key to making these machines truly useful to us, then we shall discover that a forefront-research intelligent program occupies today 3 or 4 megabytes and, incidentally, takes about 30 to 70 man-years to develop. So having a personal computer that is truly friendly and that tries to comprehend some free-format English as well as to provide certain intelligent services involves the equivalent of 4 or 5 of today's forefront intelligent programs, i.e., some 15 to 20 megabytes of primary memory. To conclude, I believe that success in distributed systems will depend on our ability to address effectively the following three challenges. First, such systems must achieve an acceptable level of overall reliability in spite of local failures. Currently computer systems are like Swiss watches.

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34 COMPUTERS OF THE FUTURE Reach into them with a spoon and the entire edifice fails, catastrophi- cally. It is essential to make distributed systems work more like human tribes- if one or more nodes collapse, the tribe goes on functioning properly. The second and perhaps biggest challenge before us is to discover a minimal semantic base, a minimal form of "computer English" that is understood by all machines and that simultaneously maximizes local autonomy and application cohesiveness. The third challenge involves the assurance that the information carried on distributed systems is protected and that the signatories of messages are indeed the purported agents and not impostors. Multiprocessor Systems The second area of myria-processor systems might be called com- putation by the yard, i.e., if you like 1 yard of computing you buy a 100- processor system, and if you like 2 yards you buy a 200-processor ma- chine. An example of a multiprocessor system is a 1,000-processor ma- chine that converts human speech to typed text. Other applications include the solution of large partial differential equations, signal pro- cessing, and weather forecasting. But the most interesting applications are in sensory computing, meaning automated eyes and ears, and in more intelligent computing. The force driving us toward multiprocessor systems is their cost. If 1,000 small processors can be harnessed into one computing machine, then that machine will have 10 times the processing power of today's fastest computer, at 1 percent of the latter's cost. This harnessing of numerous processors in one machine is being at- tempted in several ways. One way is the data-flow approach, which consists of (1) a communication network that has perhaps 1,000 inputs and 1,000 outputs, and (2) 1,000 processing elements. In this architecture the results issued by each computer enter this network carrying a little flag that establishes their destination. Thus, if the flag says "39," these results will exit the network into the thirty-ninth computer where they will be processed into new results with new flags. The programming of such a machine is entirely different from the programming of today's Von Neumann-type machines, because many operations are carried out simultaneously rather than sequentially. The challenges in trying to realize these multiprocessor systems are as follows. First, such systems must be linearly or at least quasi-linearly scalable this is the computation-by-the-yard notion. Second, as in the case of distributive systems, these multiprocessor machines must work

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SOFTWARE AND UNORTHODOX ARCHITECTURES 35 correctly in spite of local failures, because in a system with 1,000 pro- cessors there will always be several processors that do not work correctly. Finally, there must be an associated programming environment so that these machines can be effectively programmed. Moreover, such a pro- gramming environment should be "tuned" to the hardware architecture to ensure good performance under the target applications. The following question is often raised in discussions of multiprocessor architectures: It is conceivable that we can put together 1,000 or 10,000 processors, but how are such systems going to extract the parallelism inherent in today's large FORTRAN programs? My answer is that this is not possible, any more than it is possible to automatically extend procedures for managing one individual to procedures for managing a factory or a company of 1,000 people. In both cases the techniques are entirely different. Hence, we must forget about automatically unfolding the parallelism in today's programs. Instead, it is necessary to learn how to harness these "warehouses" full of computers by explicitly program- ming and organizing them in the same sense that a complex shoe-man- ufacturing company is planned and tuned today. Finally, I think that following our experience with single-processor machines there will be special-purpose multiprocessor systems dedicated to specific applications that will always carry out these applications with- out the need or ability to be reprogrammed for other applications. SUMMARY AND CONCLUSION In the software domain, programs will move from the artisan to the mass-manufacturing era, and they will manifest themselves progressively more as hidden computers or mass-manufactured applications on dis- kettes. Users will adapt to these programs rather than the other way around as has been the case in the past. Programs will become more intelligent and will move into personal computers, distributed systems, and multiprocessor systems where they will perform a variety of service- oriented functions, including the sensory area. Programming productiv- ity will not increase dramatically. Instead, the continuing large program design costs will be absorbed in the individual cost of mass-produced programs. Novel system architectures will abound under the myria-processor theme in two principal categories: (1) geographically distributed, loosely coupled systems that behave, like tribes, with autonomy and application cohesiveness and that will form an information marketplace; and (2) multiprocessor tightly coupled systems, each dedicated to one applica- tion, which are expected to open new doors in sensory and intelligent computing.

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