Thursday, February 14, 2019


The Geometry Engine was implemented as a VLSI integrated circuit in a standard 40-pin package. In order to create such a complex device, Clark and Hannah received advice and assistance from Lynn Conway who led the LSI Systems group at Xerox PARC. Conway was an acknowledged expert in VLSI design and co-author of the standard textbook on the subject, ‘Introduction to VLSI Systems’ along with Carver A Mead of Caltech. Clark and Hannah followed the book’s design methodology closely, using the example given in the book for the design of the Geometry Engine’s arithmetic logic unit. They also received support from Stanford colleague John L Hennessy, an Assistant Professor of Electrical Engineering, making use of Hennessy’s microcode simulation language known as SLIM (Stanford Language for Implementing Microcode) to create the microcode for the device.

The first working prototypes of the Geometry Engine were fabricated and tested at Xerox PARC’s Integrated Circuits Laboratory. Performance was in excess of 100,000 lines per second for a 12-device pipeline, a figure which was comparable with dedicated graphics display systems costing several hundred thousand dollars. The commercial potential of this technology was clear. In April 1981, Clark filed a US patent application for the Geometry Engine. He then set about the task of commercialising the device.