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A Historic Perspective

CAD software, also referred to as Computer Aided Design software and in the past as computer aided drafting software, refers to software programs that assist engineers and designers in a wide variety of industries to design and manufacture physical products ranging from buildings, bridges, roads, aircraft, ships and cars to digital cameras, mobile phones, TVs, clothes and of course computers! CAD software is often referred to as CAD CAM software ('CAM' is the acronym for Computer Aided Machining or Computer Aided Manufacturing). (A somewhat related concept is CIM (Computer Integrated Manufacturing).)

While he could never have foreseen today's CAD software, no CAD software history would be complete unless it started with the mathematician Euclid of Alexandria, who, in his 350 B.C. treatise on mathematics "The Elements" expounded many of the postulates and axioms that are the foundations of the Euclidian geometry upon which today's CAD software systems are built.

It was more than 2,300 years after Euclid that the first true CAD software, a very innovative system (although of course primitive compared to today's CAD software) called "Sketchpad" was developed by Ivan Sutherland as part of his PhD thesis at MIT in the early 1960s. Sketchpad was especially innovative CAD software because the designer interacted with the computer graphically by using a light pen to draw on the computer's monitor. It is a tribute to Ivan Sutherland's ingenuity that even in 2004, when operations which took hours on 1960s computer technology can be executed in less than a millionth of a second and touch-sensitive TFT combination display/input devices are readily available, there is no leading CAD software that has yet incorporated such directness into its user interface.

It is a tribute to Sketchpad's uniqueness that it defined a GUI (Graphical User Interface) more than 20 years before the term was first used.

Sketchpad was developed at MIT's Lincoln Laboratory on a TX-2 computer. The computer was very advanced for its time and had 320kb main memory, an 8Mb magnetic tape storage device, a 7 inch 1024x1024 monitor, a light pen and a button box. As with most computers of that era, programs were written in macro-assembler, punched onto paper tape and fed into the computer's paper tape reader. The computer occupied about 1,000 square feet (~93 square meters) and the 320kb memory core alone was ~1 cubic yard (~0.76 cubic meters).

Sketchpad's most incredible breakthroughs were in the way that it allowed the user to interact with the computer:

the light pen was used to draw directly on the computer's monitor and incorporated graphical user interface techniques such as rubber-banding of lines and zooming, rubber-banded lines could be constrained to always intersect at a precise angle, an advanced memory architecture was developed that allowed the creation of master objects and "instances" which were very memory efficient copies of the masters, the master-instance concept allowed the creation of a master drawing and then duplicates to be created which would inherit properties of the objects in the master drawing unless they were locally changed, if the master drawing was changed then the changes would automatically be propogated through the instances in any duplicates.

Sketchpad's drawings were created, duplicated and stored at 2000:1 scale which allowed very large layouts. Sketchpad proved beyond doubt that computers could automate repetitive design and drafting tasks with a reliability and accuracy not possible by manual methods.