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.