It's WIN.COM, by the way.
When Windows didn't have a driver for some hardware, it would tell you it's "using 16-bit driver" (or was it DOS driver?). So it's all 32-bit.
Hah, this reminds me of Win32s on Windows 3.1x...
Yes, WIN.COM was the file. All I can remember about Win32s is that it added another level of DLL hell.
The wording you're thinking of is "using MS-DOS compatibility mode"