CTSS /C-T-S-S/ n. Compatible Time-Sharing System. An
early (1963) experiment in the design of interactive time-sharing
operating systems, ancestral to {{Multics}}, {{UNIX}}, and
{{ITS}}. The name {{ITS}} (Incompatible Time-sharing System)
was a hack on CTSS, meant both as a joke and to express some basic
differences in philosophy about the way I/O services should be
presented to user programs.