> And there's no 16 bit compatibility in 64 bit Windows.

Since we're talking about the lengths Microsoft goes towards backwards compatibility: https://msdn.microsoft.com/en-us/library/aa384143(VS.85).asp...

"For older applications that use a 16-bit stub to launch a 32-bit installation engine, 64-bit Windows recognizes specific 16-bit installer programs and substitutes a ported 32-bit version."

(However, this is not always enough: https://davidcmoisan.wordpress.com/2010/02/18/16-bit-install...)

Yea that was the big break in compatibility. There's also many applications that were written for the specific hardware and many undocumented features (hacks) on 95/98 that modern Windows cannot handle.