On-Line Data-Acquisition Systems in Nuclear Physics, 1969: Chapter 2 - MULTIPLE-COMPUTER SYSTEMS

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: MULTIPLE-COMPUTER SYSTEMS

F. MULTIPLE-COMPUTER SYSTEMS

1. Introduction

At the Rutgers-Bell (RB) nuclear physics laboratory, work has been done with two different two-CPU systems. The first of these represented essentially two duplicate processors (Figure 8), and the second, now in the process of implementation, two processors of different size and capability (Figure 9). While full data are not yet available on the actual performance of the second system, an outline of the experience to date will be given.

FIGURE 8 The two-central-processor system of Rutgers-Bell.

2. Two Equivalent Processors

The initial success of the original RB SDS 910 data-acquisition system was soon tempered by a result of its popularity: during most experiments the computer was unavailable for program development or data analysis. Since most experiments required the use of displays and light pens in at least one stage of data analysis, the computer center could not handle the work.

FIGURE 9 The new Rutgers-Bell Sigma 2-Sigma 5 system.

The solution adopted was to acquire another computer with the same instruction set (an SDS 925) and to provide switches such that the line printer, card reader, and plotter could be run from either computer. No provision was made for direct transfer of data from one computer to the other.

3. Lessons from Operating Experience

In practice this system worked out quite well. There was complete interchangeability of programs from the 910 to the 925, which differed only in being five times faster. Normally the switchable peripherals were run from the 925; when the group taking data wished to print or plot current spectra, they consulted with the 925 users, then used the peripherals with little more difficulty than permanently attached units would have involved.

A further advantage of the switchable peripherals, in addition to the cost saving, was that the experiments associated with the 910 could proceed while the peripherals were being serviced. The 910 is exceedingly reliable, averaging less that one main frame failure per year, and the 925 is nearly as reliable. The vast majority of service calls have been occasioned by the peripherals and have competed with data analysis but not with accelerator utilization.

In addition to the switched peripherals, both computers were equipped with two magnetic tape transports, electric typewriter, and high-speed paper-tape reader and punch. While these units were also subject to downtime, the paper-tape system and the typewriter could be exchanged between the 910 and 925. Only the magnetic-tape transports required the use of the 910 CPU during servicing, and the presence of two transports has usually meant that the second one could carry the load until the weekly accelerator maintenance period.

While the reliability record of the central processors has been excellent, that of many of the peripherals has not. Here is an excellent justification for renting computing equipment: if units do not work well, they can be returned. For a time, a low-cost card reader (100 cards per minute) built by NCR for SDS was used. It was unacceptable in reliability and was replaced by the Univac reader which came with the 925. Another unit returned was a cartridge magnetic-tape system built by SDS. The Ampex TM-4 magnetic-tape transports on both the 910 and 925 have been consistently poor in reliability, but no other unit has been available to replace them. A manufacturer's name does not seem to be a guarantee of good 

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