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While Microsoft has been trying to push for being able to run 64-bit Windows without the 32-bit parts installed (starting with 2008 R2, the WoW64 bits are optio

While Microsoft has been trying to push for being able to run 64-bit Windows without the 32-bit parts installed (starting with 2008 R2, the WoW64 bits are optional for Server Core), I'm pretty certain that you can't (yet) get a complete interactive environment using only 64-bit mode. Just looking at the list of Microsoft applications currently running on my 64-bit Win10 desktop, there's still at least a half-dozen different Windows desktop services that are running in 32-bit mode - including the "Microsoft Bing Service". I'm sure they'll eventually want to reach a point where they can cut that off, presuming that a hybrid approach like x32 doesn't turn out to have phenomenal benefits, but it's not yet here.

0x0 10y ago
When I said removing 32bit protected mode, I meant the original 32bit protected mode which is now called "legacy mode". I believe you cannot exit long mode after enabling it, but there's a sub-mode in 64bit long mode that allows running in 32 bits - which is distinct from legacy 32bit protected mode. I guess I should have said, "leaving only long mode" (which can be 64bit or 32bit)
- rincebrain 10y ago
  Ah, my apologies. I wonder how much they'd actually save, in die area, if they removed 32bit mode while leaving in the ability to run 32bit code in 64bit mode. If it's just decoding to similar microops with slightly different parameters depending on the mode they're returning to, probably not that much, except in the decoder itself...