A lot of the holdouts are specifically z/OS mainframes running TPF. It's a distinctly different OS than z/OS (what MVS is now called). Used by VISA and the Ai

A lot of the holdouts are specifically z/OS mainframes running TPF. It's a distinctly different OS than z/OS (what MVS is now called). Used by VISA and the Airline industry. They've both had multiple attempts over the years to replace TPF, with varying degrees of success. Amadeus/Altea just barely finished getting rid of their mainframes. The other big GDS systems are still working on it. I don't think it was lack of desire or commitment of resources. ITA spent quite a lot trying to replace it, with an unusual collection of the best/brightest, and was able to replace the shopping piece successfully, but stalled on commercial success of the booking part. It's just a hard problem to solve. TPF is incredibly good at extremely high transaction rates in a distributed fashion with high reliability.