National Research Council . Ad Hoc Panel on On-line Computers in Nuclear Research

“ At the very outset of planning one should examine very closely the question of the large-scale calculating required in the overall execution of the research program of the laboratory; then, if, as usual, it turns out that a substantial amount of complex calculating is anticipated, one should consider carefully the feasibility of planning to do that part of the work at the most readily accessible computer center in the vicinity, so as to be able to concentrate one's own energies and resources, especially capital investment, on the data-acquisition system. ”

“ In order to avoid tying up a large central processor during typewriter output of masses of data, a line printer is not only very useful, it is essential for efficient operation (and to spare the typewriter) . A line printer can be immensely helpful and can save much time in the process of developing and debugging programs. The cost, however, will often preclude its addition to a modest system. If the system has an IBM-compatible tape drive, the computer output can be written on tape and later carried to a computing center for printing. ”

“ Investment in a computer system is sometimes sound because it leads to a net reduction in the overall cost of performing experiments, either by eliminating some of the labor cost, by reducing the consumption of accelerator time, or in some other way. ”

“ Since logical users within a physical user are not memory-protected against each other, they may communicate rapidly, at full machine speed. Communication between different physical users is also possible, via real or simulated I/O devices. While this system by no means guarantees execution time to any but the highest priority user, it is adequate in a single-experiment environment. The assumption is that the experimenter, who has actual control of the computer at all times, loads his logical users in the order in which he requires their priorities. ”

“ Since the ultimate criterion is research output, the role assigned to a computer system must depend on the nature of the work being planned. In some cases where a very specific use is intended, for example, in the case of a process-control application such as the Argonne plate scanner or an accelerator controller, the conditions are simple enough to make economic judgment relatively easy to apply. In the case encountered in setting up an accelerator laboratory where a wide variety of experiments is to be performed, conditions are much more complex. ”

“ The phenomenal speed of development of computer hardware, software, and methodology contributes to the difficulty experienced by everybody involved in decision-making processes regarding data-acquisition systems. Since the cost of a computer system is often a sizable fraction of the total cost of a new laboratory, there is urgent need for a set of guiding rules or principles for use by a laboratory director planning a system, a reviewer going over a proposal for support, or a potential funding agency considering proposals and reviews. ”

“ Although it may at first sight seem more economical to assemble a system within the laboratory, by use of laboratory personnel, in most cases it is now better to buy the system from a single supplier, completely installed and operable, saving one's own resources for matters more directly concerned with research. The costs in time and effort to develop a new computer system have been much larger than predicted, in almost every case known to the authors. ”

“ In a small but increasing number of cases a computer is seen dedicated entirely to a "process-control" application such as the automatic adjustment of the shim coils of a variable-energy cyclotron or the control of data acquisition in a nuclear-scattering experiment, adjustments such as changing the angle of observation being made essentially under direct automatic control of the computer. The smallest on-line systems use the smallest commercially available computers; the largest use computers bigger than those which until recently served most computing centers. ”

“ Whenever a new type of device is interfaced to a system, some form of machine-language programming must almost always be done in order to permit the handling of input-output operations involving the new device. ”

“ Software is all-important, and it is very expensive to develop, both in time and money; hence a system planner should favor a central processor for which a large amount of software is supplied by the manufacturer, especially system software. In general, when a particular type of machine has already been delivered to many customers the manufacturer may be relied upon to supply the essential software needed to run a system: an assembler, I/O routines for standard devices, and usually a Fortran compiler. ”

“ In light of the fact that only a few years back the remote computer on-line to a general computing facility was considered to be the wave of the future, with plans for such systems under vigorous discussion at many low-energy physics installations, it is at first sight surprising that there is so little progress to report at this time. The Van de Graaff accelerator laboratory at the State University of New York at Stony Brook was one such facility planning to couple a PDP-9 on hand to an IBM System 360/67 available at the university computing center. ”

“ It has also been shown quite conclusively that the ability of the physicist to program his own experiment (in Fortran) gives him enormous power, power which simply would not be available on a suitable time scale if he has to queue up for the services of a system programmer. ”

“ In medium and large systems the use of small computers for coupling input and output devices to the main computer offers a number of attractive advantages, especially now that mass production and competition have brought the prices down so low that a large amount of hardware nearly ideal for the purpose is available at a bargain. Some advantages: (1) The small machine can control data acquisition, accumulating blocks of data while the large machine is doing background calculations, interrupting those calculations only occasionally to transfer raw or partially processed data. ”

“ FIGURE 16 A data-acquisition system based on a medium-sized computer. Prices are actual costs for equipment supplied by a well-known manufacturer. This system is powerful enough to satisfy most data-acquisition needs at a typical low-energy accelerator laboratory.
The correct strategy to employ in every case should be consistent with the size of the laboratory and with the capabilities of its staff. A laboratory with a small engineering staff and with modest computing needs for the immediate future should certainly not plan to set up a large system. ”

“ Nuclear data are input by means of a general-purpose nuclear-data-acquisition interface and control unit, organized around the concept of an event, an occurrence in the real world which causes the outputs of a group of instruments selected by the user to be read into computer memory. ”

“ The physicists were not anxious to undertake what was expected to be a substantial systems program development task for the coupled system, being unconvinced that the result would be worth the effort. While they still wish to increase the computing power available to them on-site, they have elected to achieve that end by expanding high-speed core storage on their machines, at least until true time-sharing becomes available at the central computing facility. ”

“ We have now developed an assembler for the Sigma 2 which runs on the Sigma 5. The availability of card reader input and line printer output has greatly speeded Sigma 2 software development. The loading of Sigma 2 programs is also much more convenient, since they can be stored on the Sigma 5 disk and loaded exactly as Sigma 5 programs. It seems highly desirable to have an assembler for any small data-acquisition computer capable of running on another machine; the means of transporting the object code to the small computer is of less importance. ”

“ In the past few years, good and inexpensive disks have been developed which are now on the market. Some suppliers are IBM, CDC, Datadisk, Burroughs, DEC, and SDS. Disk storage is cheaper per word than core storage by two orders of magnitude; therefore, it is preferable for applications where data can be organized serially and where access and transfer [Pg 9] time requirements can be relaxed somewhat. For example, a small DEC disk system for the PDP-8 holds up to 128k 12-bit words and has an average access time of 17 μsec and a transfer rate of 16,000 12-bit words per sec. ”

“ In many cases the laboratory has a contract with an outside firm, often the computer manufacturer, for maintenance of the computer, and sometimes the rest of the system as well. In other cases all or part of this work is done by laboratory personnel. Sometimes several laboratory people are competent both in machine-language programming and in diagnosing and repairing hardware ills. Such people are very valuable, especially if they are also competent to do interfacing of new devices. ”

“ Software developed by a computer manufacturer usually takes advantage of the peculiarities of his own peripherals. If an outside device is purchased, the additional cost for programming during the lifetime of the system should be considered. If competent engineering effort is available, an interface compatible with the computer manufacturer's software may be built, with a possible saving in programming cost. ”

“ Rental rates have typically been set so that if the anticipated use period exceeds about three years, economic prudence suggests purchasing a computer rather than renting, providing that the necessary funds for capital investment are available. This can only be true, of course, because the life expectancy of modern computers is quite long, certainly over five years. (Also, one hesitates to trade in an old computer for which an excellent software collection exists!) ”

“ In ordering a new computer powerful enough to handle most of the nuclear physics laboratory's data analysis and theoretical computing tasks, cost ruled out the acquisition of a pair of program-compatible computers. ”

“ The amount of processor time available to the other users varies inversely with the experimenter's counting rate and the amount of processing he does on his data. In most experiments, the experimenter uses significantly less than 50 percent of the processor time simply because those experiments requiring the sophistication of the computer also have rather low counting rates. A priori, it is estimated that the simple priority algorithm described above is not only adequate but pays a dividend in terms of reduced system overhead time as compared to a more elaborate algorithm. ”

“ New machines will always be appealing, but the prospective purchaser must balance their appeal against considerations of probable delivery date, software availability, completeness of documentation for both software and hardware, and in general the manufacturer's support capability. Unfortunately, these factors usually weigh against a new machine. As a rule, even a medium-sized system based on a new model machine will not be in full operation for approximately one year after delivery, unless both the hardware and the software have been tried and proven in a previous installation. ”

“ The new system, with separate and nonequivalent computers, will have advantages over the old system in data analysis and general computation, because these will be done on the larger computer, either in time sharing or batch mode. Time sharing should enhance the flexibility of the system by making it easier to generate and debug new programs, in addition to improving the accessibility. ”

“ For example, one can say that experience has shown that the total investment in the computer system will be in reasonable balance with the capital investment in the bare accelerator if the ratio of costs is about one to five. ”

“ Most remote computers operate on a multiprogramming basis, hence prompt interrupts are not available. The waiting time for attention might typically be several tenths of a second, therefore the computer in the physics laboratory should be fairly powerful in order to handle the preliminary processing and buffering. With such a computer at work the necessity for fairly rapid access to the large remote machine may entirely disappear, or else the experimenter may be able to store partly processed data on magnetic tape for subsequent further reduction off-line at the computing center. ”

“ Large laboratories having strong engineering staffs are an exception; outside of industrial plants they are the places where new system development and assembly makes the most sense.
2. Large-Scale Computations and Computing Centers
In general it is best to plan to do all very large-scale computing jobs (e.g., shell model and scattering theory calculations) at a large computing center and to set up in the laboratory a system which is just large enough to handle comfortably the data-acquisition jobs. Usually a medium-sized or small system will suffice. ”

“ When working on a complicated monitor system he would be considerably less productive. System programming is obviously very expensive, therefore the average person exploring the computer market would be well advised to consider the software support along with the hardware offered in each case. Manufacturers vary greatly in this respect. A major contributing factor to the persistent popularity of the PDP-8 is that the software support is so extensive. In general, the newer a computer, the less software is likely to be available. ”

“ Planning and Procuring a Data-Acquisition System Today
It is no longer necessary to develop one's own system. Times have changed greatly. Many systems now exist which work well and are worth copying. Manufacturers and suppliers are prepared to deliver entire systems assembled and ready to operate, complete with all the necessary system software and varying amounts of utility software. ”