Advanced Micro Devices Inc (AMD)

[HailMary]

Without a recompile into a 64bit app, I would be surprised if there was much peformance *gain* for very many applications at all.

You may be right, but that was not AMD's original claim. I'll see if I can dig up a paper I read a while back stating this. Their is certainly overhead of WOW64 as you point out. Maybe AMD believed that the OS and device drivers would get a significant speedup in native AMD64 that would more than make up for the WOW64 performance hit, which may end up being true, but isn't yet. This AMD document has some details on WOW64 (google search 'AMD64 device drivers' turns this up):

http://www.amd.com/us-en/assets/content_type/DownloadableAssets/Porting_Win_DD_to_AMD64.pdf

Quote:
Porting to AMD64

Maintaining compatibility with 32-bit applications

A system call made to 64-bit Windows by a 32-bit application will require translation of its arguments such as address pointers. This translation layer is integral to the 64-bit operating system. 64-bit Windows has a layer called Windows on Windows 64 (WOW64). WOW64 is the emulation layer that enables a 32-bit application to application to operate in Compatibility
Mode when under 64-bit Windows.

WOW64 exists as a Dynamically Linked Library (DLL) that is integral to the operating system. The OS creates a separate 32-bit process to run each 32-bit application, and the thunking DLL resides within each of these 32-bit processes context. The 32-bit application is dynamically linked to the thunking layer. Each time the application executes a system call to the operating system, the thunking layer is invoked and performs the following sequence of operations:

• Translates parameters if necessary
• Transfers control to (Calls) the 64-bit kernel
• Translates the results if necessary
• Returns the results to the application

They better make sure there is no performance hit when using legacy 32-bit apps before official launch, or AMD may get some bad press.