In its original implementation, it consisted of fairly simple circuit-oriented nodes, whose circuits were created by central network supervisors 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 toward interactive character-by-character full-duplex communications 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.
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 Tymshare hosts (which ran customer code) were SDS 940, DEC PDP-10, and eventually IBM 370 computers. Xerox XDS 940 might have been used if Xerox, who bought the design for the SDS 940 from Scientific Data Systems, had ever built any.
The switches were originally Varian Data Machines 620i. The Interdata 8/32 was never used because the performance was disappointing. The TYMNET Engine, based loosely on the Interdata 7/32, was developed instead to replace the Varian 620i. In the early 1990s, newer "Turbo" nodes based on the Motorola 68000 began to replace the 7/32s. These were later replaced with SPARCs.
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.
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.
The original creators of TYMNET included: Ann Hardy, Norm Hardy, Bill Frantz. La Roy Tymes (who always insisted that his name was NOT the source of the name) wrote the first supervisor which ran on the 940. Joe Rinde made many significant technical and marketing contributions. La Roy wrote most of the code of the network proper. Several others wrote code in support of development and administration. Just recently (1999) La Roy, on contract, wrote a version of the supervisor to run on SPARC hardware.
The name TYMNET was suggested by Vigril Swearingen in a weekly meeting between Tymshare technical and marketing staff in about 1970.
[E-mail from La Roy Tymes]