.net backwards compatibility

Hi all,

I have a software company requesting we install multiple versions of .NET on client machines would the latest version 4.5.x not include all the functionality of .NET v3.5 and below as well? Or will this need individual installs of each version .NET?

Many thanks in advance.

Kind regards
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AndyAinscowFreelance programmer / ConsultantCommented:
You should just need to install the latest which would contain support for previous versions.
JohnBusiness Consultant (Owner)Commented:
I keep .NET Framework V3.5 and all its updates and V4.5 and all its updates. Those two versions are available to be enabled in Windows Features (in Programs and Features).

I do this myself and for clients and it seems to cover all the requirements.
Jacques Bourgeois (James Burger)PresidentCommented:
If you plan to recompile the old applications on framework 4.x (which I would recommend), it contains almost all the features of 3.5. A few classes are now obsolete, but a few out of more than 10,000 is almost meaningless... unless you happen to have been using one of those that were retired. I have personally never encountered any and I have converted many applications, but some of my students encountered obsolete and non-supported older classes while trying to convert old code.

Some old 3rd party dlls also do not work well if you try to use them in 4.x projects.

If you plan to leave the applications compiled as 3.5, then you need to install both versions of the framework. The version of the Common Language Runtime (CLR) that provides the basics of the framework changed in 4.0

So, in order to run on the same computer applications compiled prior 4.0 and post 4.0 you need to install both the 3.5 framework, and a version of 4.x that is compatible with your 4.x applications.

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Some object types have become deprecated (obsolete) in .Net 4.5.   If your program uses these types they may no longer function as you would expect.

Obsolete Types

Obsolete Members

fyi.... sometime around the year 2001 Sun Microsystems changed the way Java handled 'Null' values and caused my company a lot of grief.  Backwards compatibility is not always a guarantee.
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