Backwards compatibility was the one and only reason, weighting against a number of opposite considerations, that caused the industry to choose the AMD x64 architecture instead of the now extinct Itanium pushed by Intel. If the industry had been neutral towards backwards compatibility, not to mention if it had wanted to curtail it, the result would have been just the opposite.
Microsoft Windows in particular has a
remarkable record on backwards compatibility, all things considered. As for 16-bit, according to
what I've read, the main or only reason why 16-bit programs can't run natively in x64 is a technicality, that handles are 32-bit integers both in 32-bit and x64 versions of Windows (for backwards compatibility, I guess!), and so they can't be translated to old 16-bit handles.
Quote:
Originally Posted by Eagle of Fire
64 bits not being compatible with 32 bits and lower is ...
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... a wrong assertion. 32-bit programs do work in x64 OSes. And nowadays most new computers sold with Windows will have a x64 version, but most of the programs they will be used to run will probably be 32-bit. Nowadays still almost nobody's using or marketing 64-bit browsers or word processors etc. In the task manager of x64 Windows, 32-bit processes can be identified because their names have " *32" appended.
http://support.microsoft.com/kb/896456