siriusb said:
I was talking about running 32bit progs on x64 windows on an AMD64 machines. Here's an article for reference.
First of all I want to say that the test by X-bit lab was conducted on Windows XP Professional x64 Edition
RC1. It was carried out based on gaming applications.
If you are running a 32-bit program (application) on WindowsXP x64 on an AMD64 machine, it should work better. Because, as I told you —
some 32-bit applications can gain from the increased address space of the AMD64 architecture when running on a 64-bit operating system—without rewriting or recompiling a single line of code. Remember, the AMD64 architecture can run 64-bit and 32-bit applications concurrently.
Windows XP Professional x64 Edition runs 32-bit applications in the Windows on Windows 64 (WOW64) subsystem providing compatibility with the more than 10,000 existing 32-bit Windows applications while enabling new 64-bit applications.
WOW64 is the x86 emulator that allows 32-bit Windows applications to run on 64-bit Windows.
WOW64 launches and runs 32-bit applications seamlessly. The system isolates 32-bit applications from 64-bit applications, which includes preventing file and registry collisions. However, 32-bit processes cannot load 64-bit DLLs, and 64-bit processes cannot load 32-bit DLLs.
Applications running in the WOW64 system on Windows XP Professional x64 Edition each have a full 4 GB of virtual memory space. Applications compiled to take advantage of the /3 GB switch will actually get 4 GB, without constraining the operating system at all, since it is running in the 8 terabytes of virtual address space that Windows XP Professional x64 Edition has for the system processes.
But, there is one limitation:
Extensions to Windows Explorer, for example, menu extensions to the right-click menu in Windows Explorer, must be 64-bit. If they are 32-bit, the application may work, but the Windows Explorer extensions will not be available. This is because any application can be either 32-bit running in WOW64 or 64-bit. But not both. And Windows Explorer is obviously 64-bit. So the application itself will work, but the extensions won't. Hence, one can miss the right-click extensions for WinZip, a prime example of this.
Now according to Microsoft, —
execution speed of 32-bit applications under WOW64 on x64 is similar to its speed under 32-bit Windows.
On the Intel processor, more software is involved in the emulation, and
performance suffers as a result.