(Convergent Technologies OS) An operating system that runs on Unisys' x86-based NGen and SuperGen series (formerly the B-series). It was originally developed by Convergent Technologies, which was acquired by Unisys. Designed for network use, its message-based approach allows program requests to be directed to any station in the network. Client To Server In the late 1980s and early 1990s, CTOS was known informally as the "Client TO Server" environment because of its unique client/server architecture. Many clients were diskless workstations that booted from the server. Over one million CTOS/BTOS systems have been sold worldwide by Unisys. See BTOS.