A United States-wide commercial computer network created by Tymshare Inc. and used for remote login and file transfer. In its original implementation, it was made up of a number of fairly simple circuit-oriented nodes, whose circuits were created by one central network supervisor writing into the appropriate nodes' "permuter tables". The supervisors also performed login validations as well as circuit management. Circuits were character oriented and the network was oriented towards interactive character-by-character full duplex communications circuits.
There was a clever scheme to switch the echoing function between the local node and the host based on whether or not a special character had been typed by the user. Data transfers were also possible via "auxiliary circuits".
The network had more than one supervisor running, but only one was active, the others being put to sleep with "sleeping pill" messages. If the active supervisor went down, all the others would wake up and battle for control of the network. After the battle, the supervisor with the highest pre-set priority would dominate, and the network would then again be controlled by only one supervisor. (During the takeover battle, the net consisted of subsets of itself across which new circuits could not be built). Existing circuits were not affected by supervisor switches.
Tymshare Inc. originally wrote and implemented TYMNET on SDS/XDS-940 computers to provide nationwide access for their time-sharing customers. When Tymshare started using Interdata 8/32 minicomputers as nodes they started developing TYMNET on PDP-10. Tymshare sold the TYMNET network software to TRW, who created their own private network (which was not called TYMNET). In about 1979, TYMNET Inc. was spun off from Tymshare Inc. to continue administration and development of the network.
TYMNET was the largest commercial network in the United States in its heyday, with nodes in every major US city and a few overseas as well. Tymshare acquired a French subsidiary, SLIGOS, and had TYMNET nodes in Paris, France.
TYMNET has outlived its parent company Tymshare and is now owned by MCI. They still (May 1994) run three DEC KL-10s under TYMCOM-X, although they are going to be decommissioned soon.
The original creators of TYMNET include: Ann Hardy, Norm Hardy, Bill Frantz, LaRoy Tymes (who always insisted that his name was NOT the source of the name TYMNET!) and Joe Rinde, who wrote the original supervisor program.