Have a look at Windows NT 3.51 here:
Despite what I said before about this
particular version of Windows being
a 16bit OS, according to the article
at the URL above, it's 32bit OS, but
with a Windows 3.x look that makes
it look like a 16bit OS.
Now I'm not entirely sure exactly HOW
many bits make up Windows NT 3.51!
I'll have to look it up on Microsoft's
website, if I can find the time to
trawl through all of it!