C existed as a cross platform language long before there was a C standard specification or standard headers. Specifically, C was introduced around 1972 and the first standard was 1989. (Wikipedia). There were C compilers for non-Unix systems during that time (e.g., Borland Turbo C for MS-DOS around 1987). (Wikipedia).
I was using C compilers for micros well before those upstarts like Borland and MS (or even DOS) came around. The first micro I used C on was a Cromemco System III, running CP/M. That machine was built in 1977, I think, although I was using it a few years later than that.
