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Good question - what you ask is not easily answered! Even Intel is (possibly deliberately) vague about what the answer is.
Does Intel do 64-bit?
32 bit is 32 bit, 64 bit is 64 bit.
Not always so - some processors can be either 32 OR 64-bit depending on what OS is running on it! If you boot up a 32-bit OS, the processor will operate in 32-bit mode only and will NOT run any 64-bit code. You can boot the SAME processor with a 64-bit version of the OS and it will run BOTH 32 AND 64 bit code.
IO540, it wasn't the backwards compatability that allowed AMD to leapfrog intel - it was that AMD could sell a 64-bit processor that also ran 32-bit code as fast as (or faster than) a 32-bit processor.
At the time, intel's 64-bit offerings (think Itanium cores) ran 32-bit code like treacle.
There was never any question of intel 64-bit CPUs not running mainstream COTS OS and applications, just that they weren't particularly good at running 32-bit code - and there was little native 64-bit code around for them to show how good they were at that!
Intel has more than caught up with AMD - it has passed it by with its dual-core CPUs running faster and (crucially) significantly cooler, hence lower running and cooling costs.
SD