Advanced Micro Devices Inc (AMD)

[sgolds]

UpNDown, SemiconEng, AMD likes to talk about 64-bit extensions for the same reason Intel talked about 32-bit extensions when the 80386 was introduced - so as not to scare the public with thoughts of incompatibility.

However, the 80386 introduced a whole new flat mode that was unknown in the 80286 - not just a mere extension. So it is with 64-bit long mode - it is a clean break with the past, while the processor has the logic to support the older modes on board.

If one were to start fresh with a 64-bit OS and applications then it would not look very much like x86 at all!

I think that point is lost on many people, and for good reason. Should AMD stress that point, they would scare off everyone. Fortunately, they designed the processor to have the logic to run everything like a K7 or P4 (legacy mode), or to run a 64-bit OS with both 64-bit only or compatibility in long mode (64-bit OS, 64-bit, 32-bit and 16-bit applications concurrent).