TitleVideo Ethnography of "ICARUS" on the Xerox Alto
|Brock, David C., Interviewer|
|Fairbairn, Doug, Interviewee|
|Hsu, Hansen, Interviewer|
PublisherComputer History Museum
Place of PublicationFremont, CA
DescriptionICARUS (Integrated Circuit ARtwork Utility System) was a graphical integrated circuit layout design tool created for the Xerox Alto computer in the summers of 1976 and ’77 by Doug Fairbairn and Jim Rowson at Xerox PARC. The work came out of the VLSI Systems Group at PARC that was headed by Lynn Conway in collaboration with Carver Mead of Caltech, working to develop better tools and methodologies for designing chips. Rowson was a student of Meade’s at Cal Tech and worked with Fairbairn during the two summers on ICARUS’s internal algorithms while Fairbairn developed the user interface.
ICARUS’s main user interface is separated into two windows which can independently zoom into different portions of the chip. Typically, the top window was used to show a larger area of the chip while the bottom was zoomed in to a detailed view, but the windows could be used in other ways as well, such as showing the endpoints of two long lines in separate windows. Circuits are drawn with the mouse as differently patterned layers and connections, representing different physical layers and connections on the silicon chip, such as diffusion, polysilicon, metal, etc., with contacts representing vertical connection points between the layers.
ICARUS is able to save portions of a circuit as a symbol to be recalled and replicated, allowing a user to build up complex libraries of sub-circuits, in a way similar to sub-routines in software. ICARUS came out at a time when circuits were still primarily designed by hand drawing on transparent sheets of mylar, and presented for the first time a fully interactive, graphical way to design circuits in a personal workstation. An ICARUS output file would then be processed by another program to create a mask for IC production.
In this demonstration, Fairbairn designs a shift register cell with multiple transistors, saves it as a symbol in the library, mirrors the cell, makes 12 copies, and saves the entire design to a file.
ICARUS helped promote the new Meade/Conway VLSI design methodology by managing complexity through the creation of hierarchies of symbols, which encouraged regularity of structure in chip designs. This greatly simplified chip design and verification, reducing cost and errors. ICARUS was used in the design of a number of chips at PARC, including Dick Lyon’s IC for an early optical mouse, and Jim Clark’s Geometry Engine, which helped Clark launch Silicon Graphics. This use proved the viability of VLSI design methodology, which spawned custom chip design startups such as VLSI Technology, co-founded by Fairbairn with three alumni of Fairchild Semiconductor in 1979. ICARUS became the paradigmatic template for later chip design tools, creating the new industry of electronic design automation, today dominated by Synopsys, Cadence Design Systems, and Mentor Graphics.