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Designers have long used computers for their calculations. It is argued that a turning point was the development of SKETCHPAD system in MIT in 1963 by Ivan Sutherland. The distinctive feature of SKETCHPAD was that it allowed the designer to interact with computer graphically: the design can be fed into the computer by drawing on a CRT monitor with a light pen. Effectively, it was a prototype of graphical user interface, an indispensable feature of modern CAD.
Ivan Sutherland demonstrating the Sketchpad System
First commercial applications of CAD were in large companies in automotive and aerospace industry, as well as in electronics. As computers became more affordable, the application area gradually expanded.
Many CAD drawings are created from scratch using the application software using design sketches and other inputs. Other CAD drawings are created from pre-existing electronic CAD files by copying all or part of another CAD file, making changes, then saving it as a new file. Drawings that only exist in physical form (blueprints, plots of lost files, etc.) can be converted into CAD files using a procedure called "Paper-to-CAD conversion", drawing conversion, digitization, or vectorization.
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Schematic design of PCB projects 
