DAC-1

Genesis GM was an early computer user, using punched card machines as early as 1952 for engineering analysis. In 1955 they moved their computing services into the new Data Processing department of GM Research Laboratories. In 1956, together with North American Aviation, they developed the first "official" batch processing operating system for IBM systems, GM-NAA I/O. In 1958 they were one of the earliest users of IBM's new FORTRAN compiler. In June 1958 GM Research started a program to better understand the problems and potential improvements in the industrial design process. The idea was that the diagrams would be digitized into the computer, displayed interactively to allow rotations, scaling and projections, and then printed on demand. Lookups would be handled via punched card queries, which would allow operators to quickly retrieve documents for manipulation into whatever local format the user needed, and then print it. Repetitive queries could be automated simply by saving the card stack. Prototype The Data Processing department had already been experimenting with an IBM 704 computer displaying points on the IBM 780 display which were recorded to 8 mm film. One early use was plotting traffic simulations. The output was a set of cubic polynomials that described the line smoothly. DAC-1 The system, known as Digital Design, was demonstrated and improved throughout 1959. In order to avoid confusion over the term "digital", which at that time was most closely associated with fingers and not computing, the name changed to DAC-1. Once converted, the diagrams could be output into the APT numerical control language for direct output on milling machines. This would allow a design team to sketch out their ideas, put them into the system and clean them up, and then have the milling systems produce a physical model. IBM partnership In July 1960 IBM presented GM with a formal development contract for a "Graphic Expression Machine", or "Project GEM". The system was hosted by the 7090, IBM's then-standard large business offering, partnered with two new channel controllers for the yet-to-be-released IBM 1301 hard disk system, and a custom controller to drive multiple graphical terminals. Output from the terminals could be sent to a plotter, 35 mm slide film. IBM estimated the system would be installed within 18 months after signing the contract. GM accepted the offer in November 1960. Development took longer than expected. While the 7090 was being installed at GM Research in Warren, MI, the GM teams were given use of one of IBM's own 7090s in Kingston, NY. As the original production date grew closer the number of GM employees traveling to NY became a serious budget problem, which was addressed when GM rented a Convair aircraft for ferry flights between the two sites. A more serious problem was the scanner system, and a joint GM-IBM team was able to finally address the issues. The system was given a full demonstration run at IBM's Kingston site in December 1962. The demonstrations were so well attended that bleachers were set up so that all of the attendees could see the terminal screen. The high usage demands during the demos eventually led to the disk system crashing. In November 1963, DAC-1 was used to create a model of a trunk lid in a straight-through manner. An original sketch was read in, cleaned up on the terminal, converted into 3D and then output to a milling machine. Alpine With the successful delivery of DAC-1, IBM turned to commercializing the system in "Project Alpine". The results of Alpine were the IBM 2250 graphics terminal, 2280 film recorder and 2281 film scanner. Unlike the DAC-1's 7090, the Alpine products were all aimed for use with the newly announced IBM 360 series of computers. The graphics terminal was quite successful and IBM became a major CAD vendor. The film printer and scanner found little use among customers that were moving to all-digital workflows, and were later withdrawn as supported products. When polled, team leaders within the project universally pointed to the batch-oriented operating system as the primary impediment to a truly interactive design system, with computer performance and a hierarchical file system as secondary concerns. This led to the MCTS system, "Multiple Console Time Sharing System", a version of Multics adapted for their own use, which they developed on the CDC STAR-100 computer. ==Description==

Operating system The DAC-1 system included its own custom operating system, known, as was typical at the time, simply as "monitor". Monitor was based on the earlier batch processing systems developed at GM and IBM, but fed in the batches not from punched cards, but from the attached channel controllers instead. Terminals that had to exchange information with the host computer would place data in the controller for relay, which would cause an interrupt. The host machine would service the interrupt by copying the data from the terminal into the batch monitor, which would run it as if the input had come from a card stack. The DAC program consisted of a variety of small programs which were called by the batch monitor. Their output was then copied back to the terminals as if they were printers. Users who were not actively interacting with the terminals at any given time automatically gave up their time to other users. A similar language was also developed for the special task of running on the channel controllers. The new language was named "Maybe", because it was not clear whether or not it would work. Maybe turned into a joint effort between GM and the University of Michigan, and was indeed used on the production system. Performance issues limited diagrams to about 1,000 vectors; at this point the refresh time became so slow the display would become difficult to use due to flickering. The IBM design used a capacitance screen with a metal pencil for input, providing a directly read X and Y coordinate. The basic system was similar to modern touch screen systems like the iPhone, but not sensitive enough to detect a finger and instead required a wired conductor to complete the circuit. The pencil replaced the light pens because it was much faster to decode; a light pen had to wait for a pulse of light when a vector was being redrawn and then work its way through the list of vectors to find out which one was selected. In use it was quickly discovered that holding the pen to the vertical monitor screen was extremely tiring, so the idea of using the terminal for input was abandoned. The GM team later visited Douglas Engelbart's lab where they saw the first computer mouse, and based future projects on this device instead. All of the terminals were connected to a single controller, and in turn to the 7090 via its Channel C input. Channel A and B were used to control magnetic tape drives, and Channel D controlled the 1301 disk. ==References==