As of the end of last month, Autodesk is 30 years old.

What’s little known in the CAD industry, and rarely mentioned today, is that AutoCAD had an ancestor that predated the founding of Autodesk. A product called INTERACT.

This is a photo of the INTERACT CAD system, circa 1978. The hardware is an S-100 computer with dual 8″ floppy drives, and a 640×480 pixel graphics board.  Input is through a Houston Instruments digitizer and a Televideo terminal.

INTERACT was the first CAD system to run on mainstream microcomputer hardware. (Other contemporary systems ran on mainframes or minicomputers.) Its first commercial customer was Atlantic Richfield, which used the system to plan deep dives for offshore oil rigs.

INTERACT was written by Mike Riddle. He had previously worked on a ComputerVision CADDS3 system, which was used by his employer, Marathon Steel, to detail the structural steel used in the Palo Verde nuclear power plant, west of Phoenix. With the self assurance that many hackers have, Riddle figured he could do better than CADDS3.

He wrote INTERACT in his spare time, starting in 1977. He was slowed down by the state of hardware at the time — he had to write the program in pieces, and assemble it as larger memory boards became available. Ultimately, he decided he needed a processor that could support hardware multiply. Marinchip Systems, owned by John Walker and Dan Drake, made an S-100 main board with a TI TMS-9900 processor that fit the bill.

When Walker saw INTERACT running on the Marinchip Systems computer, he was impressed enough to become a dealer for the software.

In late 1981,Walker, Drake, Riddle, and about a dozen other people, came together to co-found what, in January 1982, would become Marinchip Software Partners, and shortly thereafter, Autodesk. INTERACT was rewritten in the C language, to run on the new IBM PC, and was rechristened–first as MicroCAD, and then (when the MicroCAD name was sniped by another company) as AutoCAD.

Today’s AutoCAD bears little resemblance to INTERACT.  Yet most of the original INTERACT commands still work in AutoCAD 2012.