Wow, I can tell you stories about the 5150 and it's predecessors. I worked in software development for IBM in 1980 on a temporary assignment for two years. I met Don Estridge, he gave us all plaques for our contribution to that box, mine was very, very minor, having to do with the delivery system which configured the applications. The plaque read something about "since you put everything into it", can't remember the rest, in the closet somewhere, saw it not that long ago. Too bad about Don dying in that plane accident in Texas. I still remember that day.
The team I was on, application software architecture, contributed to the decision to not pursue the OS internally within IBM. At that time we were working on manufacturing applications for the predecessor called the DataMaster. IBM didn't want to release a box without application software so there was a second team that was porting the DataMaster apps (based on MAPICS) to what was then called "the little guy". Don't remember if they ever ported them as I went back to the field sales in '82 as an SE?
Customers were buying one box at a time and running benchmarks on the interpreter BASIC. The results depended on the internal sorting of the instructions the interpreter looked up. Who would think that would make a difference today. I remember when the PC took off. I sold hundreds of thousands of those boxes thru the early years until landing in large systems.
I wonder what happened to all those PCs and the infamous Pc Jr?