1976 · Hand-Verified Mask Layout · Work 895 of 1,871
A small chip design office in California on a winter night, a large light table glowing from below, on it a milky white translucent sheet nearly one and a half metres wide, across it a faint web of pale grey-pink rectangles and narrow tracks, a dense fine grid field in its upper left corner, a ring of small square pads along all four edges, shiny pieces of clear tape at its corners, a man in a pale shirt seen from directly behind, face turned fully away, one hand holding a small clear plastic spacing gauge onto a single line, the other a pen magnifier, a paper cup of coffee, dark windows.
What it was used for
A checking drawing from the development of the Zilog Z80. The Computer History Museum lists object 102716352 as the "Z80 Mask Design Rule Check Plot", 55 inches wide and 42 inches long, weighing 1 pound, gift of Bernard L. Peuto. The plot superimposed each individual mask layer at 200 times final size so that the designer could confirm that the layout met the separations the manufacturing process required - components placed too close together will not work. Masatoshi Shima did the checking with a simple spacing gauge and spent several weeks confirming the size and spacing of each of the 8,500 transistors and all connecting lines.
What was new
What marks it is not an innovation but a method and its scale: design checking was physical work on a drawing 139.7 by 106.7 cm. The Computer History Museum gives the division of labour: Shima designed the Z80's logic and circuits, Federico Faggin - Zilog's co-founder and CEO - largely performed the mask layout himself, and that took about 15 weeks. Per the same source, automated design tools replaced this manual process in the 1980s.
What the sources leave open: A single source, and it does not date the plot itself; the page says only that the Z80 was designed at Zilog in 1976. How often checking was repeated, and how many such plots were made, the record does not say.
Connections
Every connection names its kind. “Forerunner” on its own would be a claim.
Follows fromThe 80801974The Computer History Museum calls the Z80 an enhanced, 8080-compatible processor. "It had to be compatible with 8080," says Masatoshi Shima, who developed the Z80 at Zilog after the 8080, calling it "the improved product over the 8080". On this check plot Shima verified the size and spacing of all 8,500 transistors by hand; the mask layout was largely Federico Faggin's work.Source: IEEE ETHW, Oral History: Masatoshi Shima · Computer History Museum: Z80 Mask Design Rule Check Plot (102716352)