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==Selenium diode computer logic==
In 1961 IBM started developing a low speed computer logic family<ref>https://www.google.com/patents/US3218472 US Patent 3218472: Transistor switch with noise rejection provided by variable capacitance feedback diode</ref> that used selenium diodes with similar characteristics to silicon but cost less than one cent. The [[computer terminal|terminal]] development departments were begging for low cost and didn’t need speed. It was possible to punch eighth inch discs from a sheet of selenium diode. GE claimed they could make reliable selenium diodes. They could do better than the three to five year life of selenium rectifiers but TV manufacturers liked the shorter life. {{cn|date=November 2014}} A design was achieved for a DDTL circuit with two levels of diode logic feeding one alloy transistor and no series input resistor or speed up capacitor. The family was called SMAL<ref name="ibm" /> or SMALL for Selenium Matrix ALloy Logic. The alloy transistor proved to be too fast for the selenium diode recovery. To solve this problem a selenium diode was connected around the base-emitter to slow it down. The two level logic was similar to the PLAs Programmable logic array that would come on the market many years later. Nearly any static logic function that yielded one output could be achieved with one transistor and a handful of cheap diodes. Several years later the selenium diodes indeed were not reliable and were replaced by silicon diodes. The logic family was packaged on SMS cards.<ref name="ibm">{{cite book|title=The 1060 Data Communications System|publisher=IBM|page=2|url=http://ed-thelen.org/comp-hist/IBM-ProdAnn/1060.pdf}}</ref>
==References==
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