IsOS

Declaration

BOOL IsOS (DWORD dwOS);

Parameters

The dwOS argument selects a question about the operating system, or at least about the current process’s relationship with the operating system. Rather than attempt a description of which versions, editions and other variations of Microsoft’s operating systems satisfy which questions, the following table summarises the recent implementations as generally as seems practicable. The descriptions in terms of platform, version, build, product type and suite are common to many cases, as are the descriptions in terms of system metrics, and are explained in the section on Behaviour. Such description is complete for most cases. Other cases are elaborated on separate pages.

Return Value

The function returns a non-zero value to indicate that the tested condition is satisfied, else the function returns FALSE. The non-zero value is not necessarily TRUE.

Behaviour

The function depends heavily, as might anyone, on the version information reported by the standard API function GetVersionEx. This information is sought only the first time that the IsOS function is called (per-process). The IsOS function asks first to have an OSVERSIONINFOEXA structure filled, and failing that, an OSVERSIONINFOA structure. Having got (or already having) this version information, the function sets about interpreting it for the question implied by the dwOS argument. The function returns FALSE if dwOS is not one of the supported constants.

Version Information

To save space in the preceding table, and throughout this article, some shorthands are used for the members of the version information structure and the values they can take. None should be unclear, but they are all listed below for definiteness:

• “major version” is the dwMajorVersion member
• “minor version” is the dwMinorVersion member
• “version” is a standard composition of the dwMajorVersion and dwMinorVersion members
• “build” is the dwBuildNumber member
• “platform” is the dwPlatformId member
  • “Windows” is VER_PLATFORM_WIN32_WINDOWS
  • “NT” is VER_PLATFORM_WIN32_NT
• “suite” is the wSuiteMask member, understood in terms of bit flags, so that it is whichever bits are set and it is not whichever bits are clear
  • “small business” is VER_SUITE_SMALLBUSINESS
  • “enterprise” is VER_SUITE_ENTERPRISE
  • “terminal” is VER_SUITE_TERMINAL
  • “small business restricted” is VER_SUITE_SMALLBUSINESS_RESTRICTED
  • “embedded” is VER_SUITE_EMBEDDEDNT
  • “data center” is VER_SUITE_DATACENTER
  • “single user” is VER_SUITE_SINGLEUSERTS
  • “personal” is VER_SUITE_PERSONAL
  • “blade” is VER_SUITE_BLADE
  • “storage server” is VER_SUITE_STORAGE_SERVER
  • “compute server” is VER_SUITE_COMPUTE_SERVER
• “product type” is the wProductType member
  • “workstation” is VER_NT_WORKSTATION
  • “domain controller” is VER_NT_DOMAIN_CONTROLLER
  • “server” is VER_NT_SERVER

Early Implementation

The wSuiteMask member lies in the extension from OSVERSIONINFO to OSVERSIONINFOEX, and even though the extended structure is sought by all exported implementations of IsOS, i.e., in version 5.00 and higher, this member is not interpreted until late 5.00 builds. Earlier builds work instead with a registry value:

The string data Enterprise and DataCenter are then treated as equivalent to “suite is enterprise” and “suite is data center” respectively. As with the version information, the function seeks this registry value only when first called (per-process).

Variations

In a few cases that depend solely on the (system) version information, the interpretation varies slightly with the SHLWAPI version.

Note that the change in OS_WIN2000ORGREATER (0x07) for version 6.00 makes it an alias for the undocumented case 0x04. The latter is in fact the original, dating from versions 4.71 and 4.72 when IsOS was coded in both SHLWAPI and SHDOCVW but not exported from either. The documented case 0x07 does have the merit of a better fit with the chronology of releases: case 0x04 was being used, e.g., by SHDOCVW in Internet Explorer 4.0, to distinguish “Windows 2000 or greater” some two years before Windows 2000 was released.

The change in OS_WIN95_GOLD is presumably a bug fix, the earlier coding having picked an incorrect build number.

Suite

In the following cases, which all involve testing the wSuiteMask member for a single flag, the function does not return TRUE if the flag is set, but instead returns the flag:

• OS_EMBEDDED
• OS_WEBSERVER
• OS_SMALLBUSINESSSERVER
• undocumented case 0x28
• undocumented case 0x29

System Metrics

A handful of cases are answered by calling the standard API function GetSystemMetrics to obtain a particular system metric. Where such cases are described in the preceding table as “evaluation of system metric”, it is to be understood that the IsOS function returns the metric exactly as returned by GetSystemMetrics, as opposed to returning TRUE or FALSE depending on whether the metric is non-zero or zero.

Availability

The IsOS function is exported from SHLWAPI as ordinal 437 in version 5.00 and higher. Starting with Windows Vista, the function is also exported by name.

The matter of which cases of dwOS are supported in which versions is extremely untidy—even without the variations in what is tested for each case. For the following table, a case is deemed supported if it is not coded to return FALSE trivially.

Documentation Status

Though this function dates from as long ago as 1999, it was still not documented by Microsoft in the MSDN Library at least as late as the CD edition dated January 2004.

However, the function did eventually get documented, apparently later in 2004. This article now conforms to Microsoft’s nomenclature.

Note that Microsoft is hardly rushing to keep its new documentation up to date. The several new cases of dwOS that are supported in Windows XP SP2, Windows Server 2003 SP1 and Windows Vista were not yet documented by Microsoft in the Windows Vista SDK dated January 2007.