Yes, the 64-bit SDK must be installed on a 64-bit machine, as does the
runtime. You cannot currently buy XP 64-bit but you can get it from OEMs as
part of a 64-bit computer purchase.
The 64-bit SDK contains executables compiled for 64-bit machine s(x64 for
x64 machines and ia64 for ia64 machines). The runtime does ship with a
version of csc.exe or vbc.exe for your processor that can compile for 64-bit
machines already, though. If you type, for example, "csc.exe /?" (without
quotes) you can see usage. One of the command-line options is
/platform:<type>, which you can specify x86, Itanium, x64, or anycpu. anycpu
is the default if the switch is not specified.
For this reason you really don't need the 64-bit SDK because you already
have the ability to compile for 64-bit processors if you have a version of
the 2.0 runtime installed.
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This posting is provided "AS IS" with no warranties, and confers no rights.
Software Design Engineer
Developer Division Sustained Engineering
Microsoft