[1] They were DEC PDP-11 computers (usually LSI-11 personal workstations) loaded with the Fuzzball software written by David L. Mills (of the University of Delaware).
[2][3] The name "Fuzzball" was the colloquialism for Mills's routing software.
The software evolved from the Distributed Computer Network (DCN) that started at the University of Maryland in 1973.
[3] Six Fuzzball routers provided the routing backbone of the first 56 kbit/s NSFNET,[5][6] allowing the testing of many of the Internet's first protocols.
[9] They were the first routers to implement key refinements to TCP/IP such as variable-length subnet masks.