Shuttle Astronaut Mike Mullane has some thoughts about the IBM team who built the Shuttle onboard flight software.
The people who designed, tested and supported the Space Shuttle Flight Software were the most exceptional technical team I’ve encountered.
The first version of the Shuttle flight software had two serious problems: it couldn’t fit in the computer, and it ran way too slow. IBM was two years into the contract and basically nothing worked. All hell broke loose.
By comparison to the Space Shuttle, Apollo was a Model-T Ford – no set of computer-controlled spaceship operations like this had ever been attempted. Nothing that got us to the Moon could be reused here, and so it was discarded.