More than 100 CDC 6600s were sold over the machine's lifetime. Many of these went to various nuclear weapon-related laboratories, and quite a few found their way into university computing laboratories. Cray immediately turned his attention to its replacement, this time setting a goal of ten times the performance of the 6600, delivered as the CDC 7600. The later CDC Cyber 70 and 170 computers were very similar to the CDC 6600 in overall design and were nearly completely backwards compatible.