On-Line Data-Acquisition Systems in Nuclear Physics, 1969: RELATIONSHIP TO A REMOTE COMPUTING CENTER

On-Line Data-Acquisition Systems in Nuclear Physics, 1969, by H. W. Fulbright et al. National Research Council is part of the HackerNoon Books Series. You can jump to any chapter in this book here. Chapter 2: RELATIONSHIP TO A REMOTE COMPUTING CENTER

H. RELATIONSHIP TO A REMOTE COMPUTING CENTER

1. The Small Computer with a Fast Data Link to a Remote General Computing Facility

Although the use of a small data-acquisition and experiment-control computer on-line to a remote computing center machine is not uncommon in high-energy particle physics applications, we know of few such systems presently operating in low-energy nuclear physics.

For the purposes of this discussion, we define "general computing facility" to be a relatively large-scale centralized installation charged with the responsibility of servicing a wide range of computing needs. The typical university computing center is our model for such a facility.

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 is instructive to examine what happened there. In 1967, with the completion of the new accelerator scheduled within a year, it was decided that the best way to acquire the desired power and flexibility in computing support was through a coupled system of the kind under discussion. Plans were formulated for a high-speed transmission line to a control unit on a selector channel at the computer center. Since true time-sharing of the System 360/67 was not in the offing, a 128k-byte partition of high-speed core storage was to be permanently dedicated to the needs of experimental physics (including the particle-physics group), and a high-speed program-swapping drum and at least one tape drive were to be assigned to the physics users as well.

What actually happened was that as funds became available to the low-energy physics group to implement its share of the remote link to the computer center, sentiment shifted to the point of view that the funds could more usefully be invested in a second PDP-9 installed at the accelerator, and the second small-to-intermediate class computer was in fact purchased. The two PDP-9's are coupled only by a switchable tape drive, with no plans at present for direct channel-to-channel communication. Plans for a remote link to the computing center have been completely dropped; any further funds for computing will be invested in larger high-speed core stores for the PDP-9's, at least in the foreseeable future.

Conversations with the principals involved in the operation of the Stony Brook low-energy physics facility fail to yield a clear and uniform explanation of the change in computing outlook. One cannot escape the impression that the group was not wildly enthusiastic about the proposed remote linkup in the first place, and that the evident immediate benefits to the group of a second PDP-9 on hand for program debugging and experiment setup while the second machine was running an experiment were irresistible when compared to the future promise of a remote link to the IBM 360/67. 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.

The coupled system at the University of Manitoba cyclotron is representative of what was intended at Stony Brook. At that installation, the PDP-9 is linked to the computing center's IBM 360/65 by a control unit commercially available from DEC for about $15,000. The unit connects the PDP-9 (or its successor, the PDP-15) directly to a System 360 selector channel, without requiring an additional control unit. The maximum data-transfer rate at Manitoba over a 2000-foot twisted pair cable is 50k bytes/sec. A relatively unsophisticated set of system programs has been written to control communication and transfer of data between the two computers.

The only experiment to which the coupled system (as distinct from the stand-alone use of the PDP-9) has been applied is a p-p bremsstrahlung measurement, where the data are developed in wire spark chambers and plastic scintillation counters. Information from the wire chambers defines proton trajectories, and pulse heights from the counters determine their energies. The PDP-9 first tries to reconstruct a vertex from the proton trajectories. If a point of origin can be determined for the protons to the required accuracy, the relevant coordinates for the proton trajectories and the pulse heights are sent to the IBM 360/65 for full kinematic and statistical analysis of the individual event; otherwise, the event is rejected. The large computer also prepares displays and plots of physical interest that are returned to the PDP-9 for display on the local CRT or output on the local x-y plotter.

The remote computer operates in a multiprogramming rather than in a time-shared environment, with an assigned partition of 65k bytes. Because of the well-designed program overlay feature of the 360/65 operating system, the Manitoba group does not find itself restricted by this relatively small partition. Because of other demands on the computing center, however, they are restricted in the use of this partition to 16 hours/day and 5 days/week. The operation of the coupled system is controlled almost entirely from the PDP-9 teletype, with 360/65 operator intervention required only for initial loading of the partition, off-line printout, and, of course, mounting magnetic tapes at the computing center.

Users of the Manitoba system are pleased with the cooperation and service they have received from the computing center thus far, and they are anticipating no difficulties developing as their demands on the central computing facility increase. But while use of the coupled system for experiments other than that described is clearly possible and desirable, no information was available on plans for the future.

The Brookhaven on-line remote network (Brooknet), where a pair of CDC 6600 machines sharing a common one million word extended core storage unit may be interfaced over a high-speed channel to as many as 64 remote data-acquisition computers, can be considered an extreme example of a coupled system. Although the software for Brooknet is reported to be complete and debugged, the system has not yet begun routine operation, and the first remote computer intended for low-energy physics application (a PDP-15) has not yet been delivered. (The only Brooknet user at present is the Chemistry Department, which has a remote batch terminal: teletype, card reader, and printer.)

2. Reasons for Lack of Popularity

Why has linking data-acquisition computers directly to computing centers not proved as popular as the obvious advantage of having access to an extremely powerful computer would lead one to expect? There are a number of contributing factors:

1. Since the remote computer can be used only if it is in operating condition and if the necessary personnel are present, the physicist stands to lose some of his independence and flexibility of operation (often not four-shift operation).

2. 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.

3. The total amount of time available to one user of a shared-time system per day is always limited. The amount of access time guaranteed by the computing center may not be sufficient.

4. In some cases there is a question of charges, and the total expense of involvement with the computing center may be comparable over a period of several years with the extra cost of buying a sufficiently large local computer for the laboratory to be able to handle all the essential on-line calculations. Even though the calculations may take longer in terms of machine time, they may not require as much lapsed real time if there are stringent limitations on computer center access time.

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H. W., Fulbright et al. 2013. On-Line Data-Acquisition Systems in Nuclear Physics, 1969. Urbana, Illinois: Project Gutenberg. Retrieved May 2022 from https://www.gutenberg.org/files/42613/42613-h/42613-h.htm#Page_54

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