feb 7, 1976 - Cray-1
Arguably the first ever commercially available super-computer ever. Over 100 Cray-1's were sold, making it one of the most successful supercomputers in history despite its price of $5M to $8M. The Cray-1's architect was Seymour Cray; the chief engineer was Cray Research co-founder Lester Davis. They would go on to design several new machines using the same basic concepts, and retained the performance crown into the 1990s.
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