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.