Whether to install the. Net version before running the. Net4.0 Program

There are different opinions on the Internet. MS said. net4.0 in-process side-by-side compatibility is not very clear either. The following is the actual situation I tested using a simple console program.
Test environment: Windows XP XP3 is uninstalled. other versions of net, only installed. net 4.0, The called dll is previously compiled using VS2008. (If the dll is compiled together with the source code project in the solution, the dll project version is set to V3.5, and the final program can be normal)

Console.exe	Call Assembly dll	Running result
. Net4.0	. Net 2.0	Normal
. Net4.0 Client Profile	. Net 2.0	Unable to compile
. Net4.0	. Net 3.5	Normal
. Net 2.0	None	Cannot run
. Net3.5	None	Cannot run

Result: 1. compiled.. Net 4.0 applications, do not need to install the previous version. you can also call the assembly of earlier versions. the Target is the Client Profile. 2. run the previous version. net program, you need to install the corresponding frameworkps: Microsoft. NET Framework 4 Client Profile (Standalone Installer) 41 Mhttp: // www.microsoft.com/downloads/en/details.aspx? FamilyID = e5ad0459-cbcc-4b4f-97b6-fb17111cf544

Microsoft. NET Framework 4 (Standalone Installer) 48 M

Http://www.microsoft.com/downloads/en/details.aspx? FamilyID = 0A391ABD-25C1-4FC0-919F-B21F31AB88B7reference: http://stackoverflow.com/questions/2642301/do-you-need-both-net-3-5-and-4-0-installed-or-just-net-4