https://worldhistoryproject.org/1976/2/bill-gates-writes-ope...
> Microsoft's software development [for Altair BASIC] was done on a DEC PDP-10 mainframe computer system. Paul Allen had developed a program that could completely simulate a new microprocessor system. This allowed them to write and debug software before the new computer hardware was complete. They were charged by the hour and by the amount of resources used (storage, printing, etc.) The 6800 BASIC was complete before the Altair 680B was finished.[21] This was the $40,000 of computer time [mentioned in the "Open Letter To Hobbyists"].
[snip]
> The [PDP-10] computer system was funded by the Department of Defense through its Defense Advanced Research Projects Agency. The computer was delivered in the middle of the night in 1969 at the height of the Vietnam War protests. Harvard officials were not pleased that Gates and Allen (who was not a student) had used the PDP-10 to develop a commercial product. They determined that this military computer was not covered by any Harvard policy. The PDP-10 was controlled by Professor Thomas Cheatham who felt that students could use the machine for personal use. Harvard placed restrictions on the computer's use and Gates had to use a commercial time share computer until MITS provided access to a PDP-10 in Albuquerque.
Was it wrong, legally or morally, to use a DoD-funded computer to develop a commercial product? Dunno, but the point is, Gates had access to it because he went to Harvard, and the software he developed on it got him into the position where IBM noticed him and his company.