Comment by sllabres

Space shuttle had five.

Four of them operating in a redundant set and the fifth performing non critical task, as descripted in [1]. The fifth is also programmed by a different contractor in a different programming language: #1-4 running the Primary Avionics Software System (PASS) programmed by IBM in HAL/S and #5 programmed by a different team of Rockwell International in assembly. [2]

[1] https://people.cs.rutgers.edu/~uli/cs673/papers/RedundancyMa...

[2] https://ntrs.nasa.gov/api/citations/20110014946/downloads/20...