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The most famous computer that never was. pdp-10 computers running the tops-10 operating system were labelled "DECsystem-10" as a way of differentiating them from the pdp-11. Later on, those systems running tops-20 were labelled "DECSYSTEM-20" (the block capitals being the result of a lawsuit brought against DEC by Singer, which once made a computer called "system-10"), but contrary to popular lore there was never a "PDP-20"; the only difference between a 10 and a 20 was the operating system and the colour of the paint. Most (but not all) machines sold to run tops-10 were painted "Basil Blue", whereas most TOPS-20 machines were painted "Chinese Red" (often mistakenly called orange).