From calculation to conversation
Early computers were used for calculation, with results appearing as printed numbers. The idea behind interactive drafting was different: the computer would display a drawing and respond immediately as a person changed it. That shift from batch output to a back-and-forth exchange was among the most important ideas in 1960s computing. It required a display, a way to point, and a computer fast enough to respond.
Research in this period built on earlier display work, including systems developed for air defense in the 1950s, where operators pointed at moving symbols on a screen with a light gun. Engineers realized that the same kind of equipment could be turned toward drawing.
The light pen and the display
A light pen is a pen-shaped device with a light sensor at its tip. When the pen is held against a screen, the computer can tell which part of the picture was being drawn at that moment, and so can work out where the pen is pointing. In the early 1960s, researchers at MIT used a light pen with a display on an experimental computer, in a project known as Sketchpad. A user could place lines, circles and arcs on the screen, move them, and impose rules such as making two lines meet at a right angle.
The displays of this period were generally vector displays, which drew lines directly with a beam instead of filling a grid of pixels. Lines looked sharp, but the screen had to be redrawn many times per second, which put a heavy load on the computer. If the drawing became too complicated, the image could flicker. These CRT displays were costly, and they were often attached to computers that cost far more than the displays.
The light pen was not the only input method. Early systems also used tablets, keyboards, buttons and boxes of function keys. Later, other pointing devices such as the mouse replaced the light pen in most settings, though the pen’s idea of drawing directly on the screen came back later in tablets and pen input.
What large manufacturers did with it
Interactive drafting did not start in small offices. The first industrial users were large organizations with complex products, long design cycles and the budget for expensive equipment, particularly in automotive and aerospace work.
Typical uses included:
- Drafting and revision. A designer could call up a stored drawing, change a detail and have the system redraw it, rather than redrawing the sheet from scratch.
- Curve and surface work. Car bodies and aircraft skins are defined by smooth shapes. Computers could store these as mathematical curves, then display and adjust them.
- Checking fit. A designer could look at how parts related to one another on screen before anything was built.
- Feeding manufacturing. Geometry stored in the computer could be used to prepare instructions for machine tools, a possibility that attracted manufacturers early.
Output was still often on paper. Pen plotters turned the stored geometry into finished drawings, and these were still the official documents shop floors worked from.
The experience of using an early system
Working at an early system was different from using a modern drawing program. The terminals were large and sometimes shared. The software ran on mainframe computers that served many users, and response could be slow when the machine was busy. A drawing might be stored on a magnetic disk or drum, or on magnetic tape, and loaded when needed.
Because the equipment was expensive, it was often kept busy by trained operators, not casual users. A designer might sketch on paper and have an operator enter the drawing, or might work at the console under pressure to keep a costly machine in use. The skills involved included knowledge of drafting conventions and the commands of the particular system.
Limits and early doubts
The early systems had real constraints, and honest accounts mention them.
- They were costly, so they paid off only where drawings were complex or frequently revised.
- Memory was small, which limited how large a drawing could be.
- Software was often written for one company’s computer and could not move elsewhere.
- Many drafters were uncertain about it, and there were debates about whether the new tools would help or replace skilled workers.
It would be too simple to say these systems immediately made design faster. In many cases the first benefits were more modest: greater accuracy, easier reuse of parts and the ability to store drawings as data. Larger productivity effects, where they appeared, tended to come later, when hardware became cheaper and software matured.
Why the period still matters
The ideas that emerged in this period are still visible today. Drawing as data, constraint-based sketching, display as a working surface and designs that can be revised without being redrawn all trace back to research from the 1960s. The hardware changed enormously, but the basic relationship between person and screen was established in these early experiments. The story of the first programs themselves, and the several groups behind them, is a related but separate subject; this article is concerned with how early systems were actually used.