So visual basic uses the Basic language. The same language Microsoft wrote their first dos operating system in. Wow. Never realized the history behind that! I guess Microsoft was a bit slack at writing a programming interface in the early 1990's. Instead judging by what you say, Microsoft just gave the user a copy of the tools Microsoft used. Very interesting though. Before reading your post I thought Basic was done on a teletype (i think) machine with punch cards to make slots in paper. Didn't realize that Basic had been imported as a digital language.

The first Microsoft DOS was not written in Basic, it had a Basic interpreter included (a pet project of Bill Gates then).

If the first Microsoft DOS was not written in Basic then what language was it really written in? Where punch cards still used for Bill to write the first MS operating system.

It assume it to be written in a mix of C and Assemb ly code

I think this is correct, because as my father explained to me, in those days C compilers had the inline assembly language option. This allowed access to the very low levels of the computer chips.