The Z80 was an enhanced Intel 8080-compatible 8-bit microprocessor designed by Zilog in 1976. The Z80 was extremely successful in the marketplace. Functionally equivalent processors continued to be used in new embedded designs more than 30 years after its introduction. The logic and circuit designs were implemented by Masatoshi Shima. The mask layout design, which took about 15 weeks, was largely performed by Zilog co-founder and CEO Federico Faggin. For more information see the Zilog Z80 Microprocessor Oral History Panel transcript posted at: http://www.computerhistory.org/collections/accession/102658073. This mask design rule check plot superimposed each of the individual mask layers onto a single drawing at 200 times the final size. This allowed the designer to confirm that the drawing met the specified physical separation between each component as required by the manufacturing process. If components are placed too close together they will not work. The checking task was performed by Shima. Using a simple spacing gauge, it took him several weeks to verify that the size and spacing of each of the 8,500 transistors and all the connecting lines conformed to the process design rules. This manual process was superceded by automated design tools in the 1980s.