DAC-1

DAC-1

Company type	Computer-aided design system
Industry	Computer-aided design, Engineering software
Founded	1960
Founder	General Motors, IBM
Headquarters	Warren , United States
Products	Computer-aided design platform

DAC-1, an acronym for Design Augmented by Computer, ranks among the pioneering graphical computer aided design platforms. Initially created by General Motors, IBM became a collaborator in 1960, with the system entering production by 1963. It made its public debut at the Fall Joint Computer Conference held in Detroit in 1964. GM continued to utilize and enhance DAC-1 throughout the 1970s until it was eventually succeeded by CADANCE.

Origins

General Motors was an early adopter of computing technology, employing punched card machines from as early as 1952 for engineering calculations. By 1955, computing responsibilities had transitioned to the Data Processing division within GM Research Laboratories. In collaboration with North American Aviation in 1956, GM helped develop IBM’s first official batch processing operating system, known as GM-NAA I/O. By 1958, GM had become one of the earliest users of IBM’s FORTRAN compiler.

In June 1958, GM Research launched an initiative aimed at enhancing the industrial design workflow. They observed that each phase—from conceptual styling to detailed component schematics—relied on distinct diagram formats across various departments, necessitating separate drafting teams. This fragmentation caused inefficiencies and errors when diagrams were redrawn between groups. Additionally, retrieving and updating drawings proved to be time-intensive.

Convinced that automation could resolve these issues, Donald Hart assigned GM Research’s Data Processing department in 1959 to develop a system capable of storing diagrams for rapid access and straightforward editing. The envisioned system would digitize drawings, allowing interactive manipulation such as rotation, scaling, and projection visualization, alongside on-demand printing capabilities. Retrieval would be facilitated through punched card queries that quickly fetched documents for local formatting and printing. Frequently repeated queries could be automated by preserving stacks of punched cards.

Early Development

The team had previously experimented with an IBM 704 computer that displayed points on an IBM 780 display device recorded onto 8 mm film. However, since these displays lacked storage tube technology, images faded shortly after rendering because maintaining them required continuous program loops that consumed CPU resources. A viable solution demanded hardware capable of offloading this task.

For output purposes, GM adapted a technique from Boeing, substituting the milling head of a computerized milling machine with a ball-point pen linked to the 704 computer. Due to the limited memory capacity of the 704, diagrams were segmented into 32-by-32-inch tiles designed to align seamlessly when assembled. Rollers enabled movement of a continuous paper roll beneath the plotter surface, permitting diagrams of unlimited length without needing to cut the paper.

To digitize existing paper diagrams, originals were reprinted onto transparent acetate sheets positioned over the IBM 780 display. The computer scanned a grid of dots on the screen; lines drawn on acetate blocked these dots, which were detected by a photomultiplier tube. Instead of employing slow raster scanning, whenever a line was encountered, the system scanned around that point to efficiently follow its path. This digitizer operated at speeds up to 6,000 points per second and produced output in the form of cubic polynomial equations representing smooth curves.

DAC-1

Initially named Digital Design, the system underwent refinement throughout 1959 and was renamed DAC-1 to prevent confusion with the word "digital," which at the time primarily referred to fingers rather than computing technology. By mid-year, the concept had been validated as viable, and in August, the team secured approval to partner with IBM to obtain an IBM 7090 computer and develop commercial-grade display hardware.

This production system not only processed existing drawings but also enabled in-computer modifications. Although it was not designed for generating new artwork from scratch, once diagrams were digitized, alterations could be made without the need for rescanning.

The digitized images could be transformed into three-dimensional forms—a groundbreaking feature that sparked extensive research. These 3D representations could then be converted into APT numerical control instructions, allowing direct output to milling machines. This capability empowered design teams to rapidly create physical prototypes from conceptual sketches.

IBM partnership

In July 1960, IBM extended a formal contract offer to GM for a "Graphic Expression Machine" (codenamed "Project GEM"). The system integrated the IBM 7090 mainframe with newly developed channel controllers designed for the forthcoming IBM 1301 hard disk system, alongside a custom controller supporting multiple graphical terminals. Output devices included plotters and 35 mm slide film recorders. IBM anticipated deployment within 18 months, and GM accepted the proposal in November 1960.

Development timelines were exceeded. Although the 7090 was installed at GM Research in Warren, MI, GM personnel frequently utilized IBM’s 7090 located in Kingston, NY. The necessity of frequent travel strained budgets until GM acquired a Convair aircraft for shuttle flights. Initial scanner malfunctions delayed progress but were ultimately resolved through collaboration between GM and IBM teams.

A comprehensive demonstration took place at IBM Kingston in December 1962, drawing large crowds that required bleacher seating; intensive use caused the disk system to crash. The full production DAC-1 system was launched in Warren in April 1963, initially operating with an IBM 1401 and IBM 1405 due to delays in receiving the 1301.

DAC-1 was one of the earliest commercial CAD systems, preceded only by the Itek-developed Digigraphics, which was later acquired by Control Data Corporation. In November 1963, DAC-1 successfully produced a trunk lid model by scanning a sketch, refining it on a terminal, converting it into a three-dimensional model, and outputting it directly to a milling machine.

Alpine

Following DAC-1’s successful deployment, IBM launched "Project Alpine" aimed at commercializing the technology. Alpine resulted in the creation of the IBM 2250 graphics terminal, along with the 2280 film recorder and 2281 film scanner—all tailored for use with the new IBM 360 series. The graphics terminal achieved notable market success and established IBM as a significant CAD provider. However, adoption of the film recorder and scanner remained limited as customers increasingly favored fully digital workflows; these devices were eventually discontinued.

End of DAC

From its inception, DAC was conceived as a large-scale experimental initiative rather than a fully operational production system. Despite its experimental success, further development was necessary for practical application. The CAD project formally concluded in 1967, by which time IBM had transitioned from the 7090 series to the 360 series and was advancing development on the IBM System/370. Responsibility for DAC shifted from Research to Fisher Body but was later donated to the University of Michigan due to technological obsolescence.

Project leaders identified that the batch-oriented operating system posed the greatest obstacle to achieving an entirely interactive design environment, with computer speed and hierarchical file management considered secondary challenges. This realization stimulated development of MCTS ("Multiple Console Time Sharing System"), a variant of Multics adapted specifically for use on the CDC STAR-100 computer.

Operating system

The DAC-1 operated on a proprietary system known as the "monitor," which evolved from earlier batch processing systems developed by GM and IBM. Unlike those predecessors that handled input via punched cards, this system processed data through channel controllers. Terminals communicated with the host computer using interrupts, enabling programs to run as though input originated from card decks. Output was delivered back to terminals resembling printed pages. When users were inactive, their access time was automatically reallocated to others, positioning DAC-1 as an early implementation of a time-sharing system.

Traditional batch systems were designed for predictable workloads, but DAC-1 confronted irregular demands that occasionally delayed device servicing. Although no definitive remedy was found, programmers minimized these delays by loading operational modules in grouped segments.

The initial IBM 7090 model contained a single 32 kbyte memory bank; within this, one 16 kbyte logical segment housed the DAC-1 software, while the remainder supported the batch monitor and interrupt controller. Following the upgrade to the faster IBM 7094-II, which featured two distinct 32 kbyte core memory banks, DAC-1 acquired a full 32 kbytes dedicated exclusively to its software. This enhancement boosted efficiency despite limited space available for user applications and data.

Programming

At first, programming on the DAC system relied on IBM’s FORTRAN IV compiler. However, as graphical capabilities became essential, GM adapted the University of Michigan’s ALGOL 58 derivative called MAD (Michigan Algorithm Decoder) into a customized variant named NOMAD. This language allowed flexible code execution across memory segments, a critical feature for early machines constrained by limited memory capacity. Over 90% of DAC’s software was authored in NOMAD.

In addition, GM and the University of Michigan jointly developed "Maybe," a language tailored for channel controllers, which proved effective in production environments.

The DAC-1 also incorporated DGL (descriptive geometry language), a straightforward domain-specific language offering basic geometric functions. Users could submit DGL programs via punched cards to generate new modules accessible within the interactive system.

Terminals

The DAC workflow integrated sketching, digitizing, terminal manipulation, and output through printing or modeling; however, its graphics terminal design received relatively little emphasis. The system could handle diagrams comprising up to roughly 1,000 vectors before refresh delays caused noticeable flickering.

IBM’s terminal design employed a capacitance-based touchscreen operated with a metal stylus for direct X-Y coordinate input—functionally similar to modern touchscreens but requiring a wired conductive tool rather than finger contact. This stylus replaced slower light pens that depended on vector redraw timing.

Nonetheless, holding the stylus against the vertical display proved uncomfortable over time, leading to abandonment of this input approach. After observing Douglas Engelbart’s laboratory and experiencing the first computer mouse firsthand, GM redirected future projects toward mouse-driven input methods.

All terminals were connected through a single controller interfacing with the 7090 via Channel C; meanwhile, Channels A and B managed magnetic tape drives, and Channel D controlled the 1301 disk drive.

Bibliography

• Technical Information Department, "Computer-Enhanced Design - The General Motors DAC-1 System," Search, General Motors Research Laboratories, October 1964
• Devere, G. S., Hargreaves, B., and Walker, D. M., "Overview of the DAC-1 System," Datamation, Volume 12, Issue 6 (June 1966), pp. 37–47
• J.M. Bookston, "DAC-1 Methodology for Surface Interpolation via a Network of Intersecting Spatial Curves," Research Report CT-48, General Motors R&D Center, 1968
• David Weisberg, "The Initial Commercial CAD System", 2006

Further reading

• [1] – Features multimedia content including images and videos related to DAC-1