from Charles W. McClure, April 2007 I offer the following information drawn from the "working life" of the WISC. To establish my "bona fides", I am the "CWMc" who prepared the WISC programming example included as Appendix G in the WISC Users Manual. By education I was (and remain in retirement) an electrical engineer but my interest has been in developing the programming and inter-device communication protocols which permit a number of electronic devices (computers and more specialized units) to work together towards the solution of a problem. I was a graduate student working on the WISC under the direction of Prof. Charles H. Davidson from 1959 through 1962. As will become apparent below I consider this period to be the apex of the contributions of this piece of equipment to the students and faculty of the Wisconsin School of Engineering and to Engineering Education in general. Without diminishing Dr. Amdahl's design foresight by one iota, I proffer that Prof. Davidson was the driving force that brought the WISC to fruition. For more than thirty years "Charlie" led the digital computing interests in the Wisconsin Department of Electrical Engineering and he advanced engineering education through his teaching prowess. Charlie was the author of the WISC Users Manual and developed innovative techniques to bring sophisticated computing to the engineering "masses." He believes thousands of engineering students passing of the University were introduced to computing through his formal classes and educational access to machines in the Engineering Computing Laboratory. In keeping with good graduate student traditions, my personal contributions to the WISC legacy were first in the programming arena (maintaining the library of subroutines mentioned in Appendix D of the WISCUM) and then in making some modifications to the actual machine. I added some hardware capabilities to the machine by extending the implementation of Amdahl's design in a compatible manner; the CLE instruction modified the original EXT instruction; a set of breakpoint switches was added to the console. My most significant effort was the creation of "PAT" (which stood for Pseudo Assembler Translator) as my MS thesis. PAT was a system -- a collection of routines and procedures -- which allowed third year engineering undergraduates to make use of the computer without having to master the intricacies of hexadecimal logic and subroutine calling sequences. For example, students were told about only decimal memory addresses and a TRAnsfer instruction was inserted into each address ending in hex 'a'. At that time (1960) the prevailing wisdom was that a person should not utilize a computer as merely a tool until and unless they understood the inherent limitations of the logic design -- accuracy (round-off in floating point calculations), efficiency considerations, and monitoring for hardware malfunctions. PAT allowed students to make use of the computer through a couple of three hours labs in the same way they were already using a slide rule (even though few could explain the nuances of log-log scales and keeping track of the decimal point -- and essentially none ever saw a circular slide rule!). The students and faculty were sufficiently interested in this new tool that a commercial computer was soon acquired and the WISC was supplanted for undergraduate use. The WISC had a few attributes which should be mentioned before all memory of that era is lost: A tone generator was connected to the instruction decoder and fed a speaker on top of the main frame. After a few hours of listening to the "music of the beast" it was possible for humans to deduce what the machine was doing; it was possible for a person to recognize that an iteration was not converging or that the machine had reached the final steps of producing output. Some users had special routines solely to produce musical passages as the program transitioned from one step to another. It should be emphasized that paper tape was the input and output medium; the input tape was created using a Friden Flexowriter (which was entirely separate from the machine) and the readable output was printed by feeding the output tape through this same device. There was no Teletypewriter associated with the WISC during its tenure at the University. The Engineering Research Associates magnetic drum was the heart of the WISC and was mounted under the main frame. The bearings supporting the drum and its attached motor tended to leak lubricating oil into the drum housing and the oil would gradually collect in the bottom of the [horizontally positioned] drum. Therefore occasionally the accumulated oil had to be drained from the drum but no drain plug had been provided; it was necessary to unscrew the bottom-most read/write head. Reinstalling the head was no picnic since it was only a few inches from the floor, goopy oil would continue to leak until the head was fully seated, the threads were delicate and could have been easily damaged, and if the head was advanced too far it would come in contact with the surface of the drum -- thus quickly grinding away the magnetic coating on the drum. The final adjustment was done with an oscilloscope monitoring the signal from the head as the drum spun a few thousandths of an inch away from the head mechanism; close meant a strong signal -- too close meant squealing sounds and no signal. The reliability and stability of vacuum tubes required some careful maintenance procedures. One of the permanently stored subroutines was a quick test of the basic functions. Good programming practice demanded that programs include back-up procedures and exercise this internal test at a frequency determined by the importance of the programming output. Start-up each day involved powering up up some 1000 tubes and this warmup took a half-hour or more. During this period the internal test was run repeatedly until consistent results were achieved; then a more complex program (a Runga-Kutta solution to the differential equations of a bouncing ball was a favorite) would demonstrate whether the machine could be trusted. The WISC power supplies had a provision for varying the delivered voltages so aging tubes might be coaxed into failing while running diagnostics rather than during useful execution. The logic modules required selected tubes whose characteristics were well matched; keeping a stock of spare modules was a job assigned to undergraduate students paid on an hourly basis. A thousand vacuum tubes generate a lot of heat. A [noisy] air conditioning unit kept the room bearable during Wisconsin summers. During winters we opened the windows to reduce the demands on the air conditioning equipment but it was often the case that the AC was running while the windows were open on a cool autumn day. The final check of the evening was to shut the windows when the mainframe was turned off. Temperature control became more of an issue when another computer (an IBM 1620) was installed in the same room. I hope these reminiscences can somehow be added to the historical record of the WISC. I would suggest that Charlie Davidson could provide much in the way of context. I believe his PhD thesis was one of the first ever devoted to programming as an intellectual activity. I will make it a point to visit the Computer History Museum if ever I am in the area. Charles W. McClure 50 Concord Street Newton, MA 02462-1004 617-244-3963 cwmcclure@yahoo.com