Geoff Chappell - Software Analyst
The IsOS function supports 0x28 as its dwOS argument but for two entirely unrelated questions about the operating system. Which question is answered depends on which version of SHLWAPI is asked.
To version 6.0 from Windows Vista, and higher, case 0x28 asks whether the operating system is 64-bit Windows. The 32-bit SHLWAPI tests whether the current process is running on WOW64, as for OS_WOW6432. The 64-bit SHLWAPI simply returns TRUE.
To earlier builds of version 6.0, case 0x28 is answered from the version information obtained from the standard API function GetVersionEx, specifically whether the wSuiteMask member has VER_SUITE_STORAGE_SERVER set.
Case 0x28 of the SHLWAPI function IsOS is supported in version 6.0 from Windows Server 2003 SP1, and higher.
This case is undocumented, at least as late as the Windows Vista SDK dated January 2007. The name OS_WIN64 is invented, pending discovery of Microsoft’s name.