The Win32 API. E.g. using WriteFile to write files (https://learn.microsoft.com/en-us/windows/win32/api/fileapi/...)
It wasn't until fairly recently that the C runtime was stably shipped with Windows. Previously you had to install the correct version of the C library alongside your application.
It wasn't until fairly recently
By "recently" you mean Win95? MSVCRT.DLL has been there for at least that long.
> The Win32 API. E.g. using WriteFile to write files (https://learn.microsoft.com/en-us/windows/win32/api/fileapi/...)
Which is called from what, if not C? Does windows really offer no API for writing text (rather than bytes) to files? Or does it rely on the application developer to manage line endings in their own code? Neither of those sounds very developer-friendly.