Is .Net 4.0 Compatible with Windows Xp Sp2 or Below

Is .NET 4.0 Compatible with Windows XP SP2 or below?

.NET 3.5 will give you compatibility with XP SP2. If you want compatibility with any level of XP, you need to go all the way back to .NET 2.0.

.NET 3.5 requirements can be found here:
http://msdn.microsoft.com/en-us/library/cc160717(VS.90).aspx

.NET 3.0 requirements can be found here:
http://msdn.microsoft.com/en-us/library/aa480198.aspx

What versions of Windows will .Net 4.0 support?

The official list is here.

Supported operating systems are:

Windows XP (SP3)
Windows Vista (SP1)
Windows 7
Windows Server 2003 (Base & R2)
Windows Server 2008 (Base & R2, all editions, not supported in Server Core Role)
Windows Small Business Server 2003 & 2008

Notable operating systems not supported include XP Media centre edition, XP Tablet PC edition and Windows 2000.

(The .NET Framework Client Profile is not supported on IA-64 systems.)

[Updated list for final release]

~~(see here (beta 1))~~
~~(see here (beta 2))~~

Does windows XP SP2 include .net framework by default?

No, it doesn't contain it. I hope 3.5 is delivered with Windows 7 though. Any Words on that?!

Here is an actual overview which Windows Version included a .Net Version

.Net Versions (Wikipedia)

Fully understanding the .NET versions and backward compatibility

As far as I know, the only thing that's not backward compatible is the CLR version, which is changed after .NET 4.0.

This isnt true. You can make your .NET2 compiled application run on the .NET4 framework.

You just need to add the following to your app.config:

<configuration>
<startup>
    <supportedRuntime version="v2.0.50727"/>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0,Profile=Client"/>
    <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
  </startup>
</configuration>

Note, I agree with @KingKronus, ie Why not just pick the lowest common denominator?

In your case that would be .NET2 compiled and only one set of pdbs and one compilation set.

Yes, you would need to test your .NET2-compiled app runs OK on the .net4 runtime BUT you would need to test your app in each of the frameworks in your original solution anyway.

Highest .NET version supported by Windows XP

Depends on the version of Windows XP you have, "Windows XP Home Edition" and above supports up to .NET 4.0 while "Windows XP Home Reduced Media Edition" only supports up to .NET 3.5, see the link below for the specific version of .NET supported on different editions of Windows XP.

.NET Framework System Requirements

OS Compatibility for various .NET Framework versions

1.x and 2.0 work all the way back to Win98 but stop before Windows 8 (not verified).

.NET Framework 2.0 Supported Operating Systems according to Microsoft:

Windows 98
Windows ME
Windows 2000
Windows XP
Windows Vista (included with OS)
Windows Server 2003
Windows Server 2008 (included with OS)

.NET Framework 3.0 Supported OSs:

Windows XP SP2
Windows Vista (included with OS)
Windows 7
Windows 8
Windows 2003 Server Service Pack 1 (SP1)

Note: Windows Vista comes with .NET Framework 3.0. Standalone .NET Framework 3.0 packages are not required and not supported on Vista.

.NET Framework 3.5 Supported OSs according to Microsoft:

Windows XP
Windows Vista
Windows 7 (included with OS)
Windows 8 & 8.1 see
Windows Server 2003
Windows Server 2008
Windows Server 2012 & 2012 R2 see

.NET Framework 4.0 Supported OSs according to Microsoft:

Windows XP (but not Starter, Media Center or Tablet editions)
Windows Vista
Windows 7
Windows 8
Windows 10
Windows Server 2003
Windows Server 2008

.NET Framework 4.5 Supported OSs according to Microsoft:

Windows Vista SP2
Windows 7
Windows 8 (included with OS)
Windows 10
Windows Server 2008 SP2/R2
Windows Server 2012 (included with OS)

.NET Framework 4.5.1/4.5.2/4.6 Supported OSs according to Microsoft:

Windows Vista SP2
Windows 7 SP1
Windows 8
Windows 8.1 (included with OS)
Windows 10 (4.6 included with OS)
Windows Server 2008 SP2/R2
Windows Server 2012 (included with OS)

What version of the .NET framework is installed on Windows XP, Vista, and 7?

From Wikipedia and MSDN:

.NET Framework 1.1: Windows Server 2003
.NET Framework 2.0: Windows Server 2003 R2
.NET Framework 3.0: Windows Vista, Windows Server 2008
.NET Framework 3.5: Windows 7, Windows Server 2008 R2
.NET Framework 4.0: n/a
.NET Framework 4.5: Windows 8, Windows Server 2012
.NET Framework 4.5.1: Windows 8.1, Windows Server 2012 R2
.NET Framework 4.5.2: n/a
.NET Framework 4.6: Windows 10
.NET Framework 4.6.1: Windows 10 v1511
.NET Framework 4.6.2: Windows 10 v1607, Windows Server 2016

.NET Compact Framework 1.0 (SP2): Windows Mobile 5.0
.NET Compact Framework 2.0: Windows Mobile 6.0

From other SO questions:

Windows 7 - 3.5
Vista - 2.0 and 3.0
XP - not installed
XP SP2 - not installed
XP SP3 - not installed

If you want to be certain that you application runs on all of these, you will have to install the framework yourself - use SmallestDotNet.com for this.

Is .Net 4.0 Compatible with Windows Xp Sp2 or Below