The setup wrapper for the .NET Framework 2.0 performs several system and prerequisite checks before it allows the user to start installing.  This blog post will explain the implementation details of each of the checks that .NET Framework 2.0 setup performs behind the scenes so that you can implement your own checks or enforce higher prerequisite levels if necessary.

If you are planning to deploy the .NET Framework 2.0 to your network or include it as a prerequisite in your setup package, it is very important that you understand what these checks do so that you can verify that the computers on your network will meet the minimum system requirements and deployment will be able to proceed correctly.

In addition, if you are planning to install the .NET Framework 2.0 in silent mode as a part of your installation package, you must be able to check for these conditions yourself or be able to handle cases where these conditions are not met and .NET Framework 2.0 setup fails as a result.

Single instance of setup check

.NET Framework 2.0 setup attempts to acquire a mutex at the beginning of execution.  If it is already owned by another process, it exits and tells the user that another instance of setup is already running.

Administrative privileges check

.NET Framework 2.0 setup uses the algorithm documented in this knowledge base article to check whether or not the setup process has the necessary administrative privileges.

OS version check

.NET Framework 2.0 setup first calls the GetVersionEx API.  If the dwPlatformId member of the returned OSVERSIONINFO structure equals VER_PLATFORM_WIN32_WINDOWS, then the OS version is Windows 9x and the OS version check is done.

If dwPlatformId equals VER_PLATFORM_WIN32_NT, then setup checks the dwMajorVersion and dwMinorVersion members of the returned OSVERSIONINFO structure.

If dwMajorVersion < 5, then setup blocks installation because Windows NT 4.0 and earlier versions of Windows NT are not supported platforms for installing the .NET Framework 2.0.

If dwMajorVersion is greater than or equal to 5, then the OS is a valid OS to install the .NET Framework 2.0, and the following logic is used to determine exact OS version:

• Windows 2000: if dwMajorVersion = 5 and dwMinorVersion = 0
• Windows XP: if dwMajorVersion = 5 and dwMinorVersion = 1
• Windows Server 2003: if dwMajorVersion = 5 and dwMinorVersion = 2

64-bit OS check

The .NET Framework 2.0 shipped both as 32-bit and 64-bit packages.  Setup requires that the version of the .NET Framework 2.0 that matches the current processor architecture be installed, and attempting to install mismatched versions will be blocked.

The 32-bit version of .NET Framework 2.0 setup blocks the user from installing on a 64-bit OS.  It does this by checking to see if the current setup process is running in the WOW64 layer.  To do this, .NET Framework 2.0 setup attempts to locate the GetSystemWow64Directory API.  If this API exists on the system and it returns a valid path, then setup reports that the system is a 64-bit OS and the current instance of setup is a 32-bit process running in the WOW64 layer, and it blocks the user from installing.

The 64-bit version of .NET Framework 2.0 setup will not run on a 32-bit OS.  There is not a specific block implemented in setup for this.  Instead, setup will display a generic error just like all 64-bit executables do when they are launched on a 32-bit OS.  It could be one of the following:

• If setup is launched from the self-extracting EXE: Error creating process <C:\DOCUME~1\username\LOCALS~1\Temp\IXP000.TMP\Install.exe>.  Reason: C:\WINDOWS\system32\advpack.dll
• If setup is launched by running install.exe directly: install.exe is not a valid Win32 application.
• If setup is launched by running msiexec.exe /i netfx.msi: This installation package is not supported by this processor type. Contact your product vendor.

Check to see if the .NET Framework 2.0 was installed as part of the OS

.NET Framework 2.0 setup checks to see if it is being run on an OS that already has the .NET Frameowork 2.0 installed as part of the OS.  To do this, it checks the following registry value:

• Key name: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\NET Framework Setup\NDP\v2.0.50727
• Value name: OCM
• Value data type: REG_DWORD
• Value data: 1

Currently, the only OS that includes the .NET Framework 2.0 is Windows Vista.  However, that could change in the future, so the safest way to detect whether the .NET Framework 2.0 is installed as an OS component is to check the above registry value as opposed to trying to detect the OS version.

Microsoft Internet Explorer 5.01 version check

.NET Framework 2.0 setup verifies that the version of Internet Explorer installed on the system is at least version 5.01.  To do this, it checks the following registry value:

• Key name: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer
• Value name: Version
• Value data type: REG_SZ
• Value data: greater than or equal to 5.0.2919.6307

Note that this check requires splitting the Version registry value into 4 different parts by splitting on the period and comparing each part of the version against the minimum values 5, 0, 2919 and 6307.  A simple string comparison will not work because, for example, version 2.0.0.0 would be greather than 10.0.0.0 when using a string comparison.

Windows Installer version check

.NET Framework 2.0 setup validates the Windows Installer version installed on the system.  To do this, it first determines the location of msi.dll by checking the following registry value:

• Key name: HKEY_LOCAL_MACHINE\ SOFTWARE\ Microsoft\ Windows\ CurrentVersion\ Installer
• Value name: InstallerLocation
• Value data type: REG_SZ

The InstallerLocation value will contain a folder path.  .NET Framework 2.0 setup then appends msi.dll to the value of the InstallerLocation value, and loads and attempts to call the DllGetVersion API in msi.dll.  If that API returns success, setup checks for the following return values:

• If the OS is Windows 9x: dwMajorVersion is greater than or equal to 2 and dwMinorVersion is greater than or equal to 0
• If the OS is Windows 2000 or later: dwMajorVersion is greater than or equal to 3 and dwMinorVersion is greater than or equal to 0

Note that while the initial .NET Framework 2.0 setup only checks for Windows Installer 3.0 or later on Windows 2000 and later, hotfixes and service packs for the .NET Framework 2.0 will require Windows Installer 3.1 or later in order to install correctly.  As a best practice, your setup should enforce that Windows Installer 3.1 is present as well.

Previous beta product check

.NET Framework 2.0 setup uses the algorithm in this blog post to check for previous beta products that are installed on the system.

.NET Framework 2.0 already installed check

In order to determine whether or not to enter maintenance (repair/uninstall) mode or not, .NET Framework 2.0 setup checks to see if the .NET Framework 2.0 MSI is already installed on the system.  It retrieves the product code for netfx.msi, then calls the MsiQueryProductState API and passes in this product code.  If MsiQueryProductState returns INSTALLSTATE_DEFAULT, then setup enters maintenance mode.  Otherwise, setup enters initial install mode.