Windows PowerShell 4.0 is part of the Windows Management Framework 4.0, which includes the following:
Operating system
Windows PowerShell 4.0 available
Prerequisites
Installation file
Windows Server 2012 R2
Built-in
N/A
Windows 8.1
Windows Server 2012
Yes, part of WMF 4.0
.NET 4.5 (built-in)
x64: Windows8-RT-KB2799888-x64.msu
Windows 8
No, user must upgrade to Windows 8.1
Windows Server 2008 R2
Windows Server 2008 R2 SP1
.NET 4.5
x64: Windows6.1-KB2819745-x64-MultiPkg.msu
Windows 7
Windows 7 SP1
x86: Windows6.1-KB2819745-x86.msu
Installation succeeds even if .NET 4.5 is not installed
Scenario: Installing WMF 4.0 on a computer that is not running .NET Framework 4.5 will report that the installation is successful, but the components of WMF 4.0 (such as Windows PowerShell, WMI, etc.) will not be updated.
Solution: Install .NET Framework 4.5, and then run the WMF 4.0 installer again.
http://blogs.msdn.com/b/powershell/archive/2013/10/29/wmf-4-0-known-issue-partial-installation-without-net-framework-4-5.aspx
There are known compatibility issues with several Microsoft server-class applications:
Read the WMF 4.0 Release Notes for more information.
Update is available that prevents the PSModulePath environment variable from being reset when you upgrade WMF 3.0 to WMF 4.0 and then uninstall WMF 4.0 in Windows http://support.microsoft.com/kb/2872047
Update prevents the “PSModulePath” environment variables from being reset after you uninstall WMF 4.0 in Windows
http://support.microsoft.com/kb/2872035