It ran on the NuMachine and had remote procedure call functionality built into its kernel, but was otherwise a Version 7 Unix workalike.
[1] User space programs could create threads through a spawn system call.
[2] Indeed, TRIX's original design used a nonblocking message passing mechanism,[2] but "this implementation was found to have deficiencies often overlooked in the literature,"[2] including poor performance.
The mutual exclusion primitive could be ported to any architecture with an atomic test and set instruction.
[4] In a speech in October 1986, Stallman elaborated that "the TRIX kernel runs, and it has a certain limited amount of Unix compatibility, but it needs a lot more.