function IsWin64: Boolean;
Returns True if the system is running a 64-bit version of Windows. If False is returned, you cannot utilize any of Inno Setup's 64-bit-only features.
Another way to describe this function is: Returns True if the system matches architecture identifier win64.
Do not use this function to detect 64-bit install mode, use Is64BitInstallMode instead.
begin
// Check IsWin64 before using a 64-bit-only feature to
// avoid an exception when running on 32-bit Windows.
if IsWin64 then
begin
MsgBox('64-bit program files reside in: ' +
ExpandConstant('{autopf64}'), mbInformation, MB_OK);
end;
end;