The first working version of S was built in 1976, and operated on the GCOS operating system. At this time, S was unnamed, and suggestions included "ISCS (Interactive SCS)", "SCS (Statistical Computing System)", and "SAS (Statistical Analysis System)" (which was already taken: see SAS System). The name 'S' (used with single quotation marks until 1979) was chosen, as it was a common letter in the suggestions and consistent with other programming languages designed from the same institution at the time (namely the C programming language).