Mailbag: Do I need still need older versions of the .NET Framework on my system after installing the .NET Framework 4?

Note: This is an updated version of a previous mailbag entry that I posted before the .NET Framework 4 shipped.


I recently installed the .NET Framework 4 on my system. Afterwards, I looked in Add/Remove Programs, and it shows that I have all of the following versions of the .NET Framework installed on my system:

  • Microsoft .NET Framework 1.1
  • Microsoft .NET Framework 2.0 SP2
  • Microsoft .NET Framework 3.0 SP2
  • Microsoft .NET Framework 3.5 SP1
  • Microsoft .NET Framework 4 Client Profile
  • Microsoft .NET Framework 4 Extended

Do I need any of these older versions of the .NET Framework now that I’ve installed the .NET Framework 4, or can I safely uninstall them?


In general, my recommendation is to leave the .NET Framework 2.0 SP2, 3.0 SP2, 3.5 SP1 and 4 installed on your computer.

Unlike previous versions of the .NET Framework, the .NET Framework 4 does not allow an application that was built with previous versions of the .NET Framework to migrate forward and run on it if the previous version is not installed. If you are using any applications that were built with any version of the .NET Framework before version 4, then I recommend leaving both the .NET Framework 3.5 SP1 and the .NET Framework 4 installed.

You cannot use the .NET Framework 3.5 SP1 unless you also have the .NET Framework 2.0 SP2 and 3.0 SP2 installed. Therefore, you will not be allowed to uninstall the .NET Framework 2.0 SP2 or 3.0 SP2 if you have the .NET Framework 3.5 SP1 installed. If you try to uninstall the .NET Framework 2.0 or 3.0 when the .NET Framework 3.5 is installed, their uninstall processes will block and tell you that they are needed by another application on your system.

The .NET Framework 1.0 and .NET Framework 1.1 can be installed side-by-side with the .NET Framework 2.0, 3.0, 3.5 and 4. Most applications that were created for the .NET Framework 1.0 or 1.1 will automatically use the .NET Framework 2.0 instead if it is installed on the system. In most cases, that means you do not need to keep the .NET Framework 1.0 or 1.1 installed on your system if you already have the .NET Framework 2.0 installed.

However, there are some applications that are configured to require a specific version of the .NET Framework, even if later versions of the .NET Framework are installed. If you have any applications like that on your system and try to run them without installing the .NET Framework 1.0 or 1.1, you will get an error message that looks like the following:

MyApplication.exe - .NET Framework Initialization Error
To run this application, you first must install one of the following versions of the .NET Framework:
Contact your application publisher for instructions about obtaining the appropriate version of the .NET Framework.

In the above error message, the version number will be v1.0.3705 if you need to install the .NET Framework 1.0, and it will be v1.1.4322 if you need to install the .NET Framework 1.1.

If you end up seeing any error messages like this, you can re-install the .NET Framework 1.0 or 1.1 in order to resolve the errors. If you don't end up seeing any error messages like this, then you don't need to worry about re-installing the .NET Framework 1.0 or 1.1.

Comments (28)
  1. Michael Gonseth says:

    Thank yo for the info it was very helpful. Wish they could do like java and do away with the previous versions.

  2. Anonymous says:

    Great answer, Thanks! I wish I didn't need the older versions, though. :(.

  3. royi says:

    where did you read that " .NET Framework 4 does not allow an application that was built with previous version"

  4. Hi Royi – This behavior is described in the Application Compatibility and Deployment section of the MSDN page at…/ms171868.aspx.

  5. Richard L says:

    I agree one would think a step forward in the Net framework would be a step forward not just another bundle of updates and patches and so forth.

    I look at how practically most of the software is filled with Microsoft junk.

    Good system too much baggage.

    Net 4 should be all inclusive in order to do away with the early Packs.

  6. B says:

    Completly agree with the other posters, in that it should be more like Java. It can be a pain trying to manage a system that has all these installations. Add in all the C++ redistributables & the machine I'm looking at now has over 15 instllations just from .net & C++.

  7. Aziman says:

    thanks for these helpful tips…

  8. BH Cheong says:

    Thank you very much for the informative explanation.  I was almost framed to remove all the pervious .NET Framework.  🙂

  9. Seth D says:

    Thank you as well!  I also was going to remove them prior to your information.  Very helpful to me and very much appreciated.

  10. Joseph says:

    Thanks for the very informative answer! I was cleaning up unused programs and stumbled upon the .net frameworks. I was about to delete them. Good thing I didn't.

  11. Saradhi says:

    i too had 2.0,3.0,3.5 in my xp with sp3. i downloaded manually 1.0 and left it. but windows update installed the remaining. but i am not a developer. i removed 1.0 but i now understand why i cannot remove the remaining. What type of applications use this framework?

  12. Hi Saradhi – You can find more information about what types of applications use the .NET Framework at…/.NET_Framework.

  13. Robert Feal-Martinez says:

    Hi Aaron,

            Came across this thread because having trouble .net 2 hogging CPU. None of the fixes worked. I note you stated that various versions don't replace other, and yet you wikipedia link seems to be saying in most cases they do.

    For non techies this is of course confusing. Could you please clarify.

  14. Hi Robert Feal-Martinez – Some of the information about replacing/superseding in the Wikipedia article isn't exactly right.  The .NET Framework 3.5 requires both the .NET Framework 3.0 and 2.0 behind the scenes, and the .NET Framework 3.0 requires the .NET Framework 2.0 behind the scenes, so 3.0 and 3.5 don't supersede 2.0.  Also, the .NET Framework 1.1 is a side-by-side version and doesn't supersede 1.0.

    I'm not sure I understand your CPU hogging problem though.  The .NET Framework is not an application, it is a framework used by applications.  Is there a specific .NET Framework application that is hogging CPU on your computer, or does that happen for all .NET Framework-based applications?

  15. Burak says:

    Thank you ?+)

  16. tino says:

    I dont agree . I intalled only framework 4.0 and ewerything is running smooth. Now im going to install 4.5.1 but keep 4.0 on my comp for a while but thats why im here on this site ,to hear what u all think.  

  17. Hi tino – The .NET Framework 4.5.1 is a full replacement for the .NET Framework 4 that includes new features and bug fixes.  You can't have both the .NET Framework 4 and the .NET Framework 4.5.1 installed on the same computer at the same time.

  18. Christian says:

    Hi Aaron,

    thanks a lot for your very helpful informations. Yesterday I installed Windows 7 and Office 2010 and nothing else. Do I really need apart from .NET Framework 4.5.1 also the older version 3.5.1? Because Windows every time shows about 17 updates for .Net Framework 3.5.1 as important updates. Do Windows and Office need this old version for themselves?

  19. Hi Christian – Windows 7 includes the .NET Framework 3.5 family as a part of the OS.  You can enable/disable the .NET Framework 3.5 by using the Windows Features control panel, but you can't enable/disable the .NET Framework 2.0 or 3.0.  Because of that, there won't be any way for you to prevent Windows Update from listing those updates for the .NET Framework 3.5.1 on your computer.

  20. Christian says:

    Hi Aaron,

    thank you very much for your very competent answer.

  21. Hernan says:


  22. SadNBad says:

    No, 4.5 doesnt include 4.0 and haven't got back compatibility. I have 4.5 installed and can't install directx because it requests exactly 4.0. More to say my 4.5 install was made on system with 4.0 installed. So stop believing MS employees incompetent BS they feeding us last 20 years.

  23. Hi SadNBad – The .NET Framework 4.5 download page at…/details.aspx says that the .NET Framework 4.5 is a highly compatible in-place update to the .NET Framework 4.  That means that the .NET Framework 4.5 does include .NET Framework 4 functionality, and apps built against the .NET Framework 4 will continue to work fine when the .NET Framework 4.5 is installed in nearly all cases.

    If you're seeing an installer detect that you need to install the .NET Framework 4 when the .NET Framework 4.5 is already installed, that is nearly always an application compatibility bug in the application itself, and I'd recommend looking for known issues, workarounds, or patches on the web site for the application's manufacturer.

  24. kishor mane says:

    why microsoft was not provided .net framework 1.0 & 1.1?? is there any problem in that framework?

  25. Wills661 says:

    I now understand Why the frameworks are installed every hour on my computer but the updates never increase in number, I have 279 updates showing on my computer and windows adds 5 more but the number never changes.

  26. Hi kishor mane – I'm sorry, but I don't understand your question.  You can download the .NET Framework 1.0 from…/details.aspx and the .NET Framework 1.1 from…/details.aspx if you need them.

  27. Hi Wills661 – The behavior you describe sounds like one of the first Windows Updates in your list is failing, and then it doesn't go on and try to install the later ones in the list.  Do you know which exact update is failing?  You might be able to find more detailed error information by looking for log files for the failing update in your %temp% directory and/or by looking in the file %windir%WindowsUpdate.log.

  28. Bill says:

    Just use Delphi and end this .Net nonsense.

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