install iphone sdks side by side

Question

Im trying to get my xCode to contain all iPhone sdk's from 4 back to 2. But when I download the DMG files, it seems to only allow me to have an xCode with SDK versions 2 - 3.1 OR 3.2 - 4, not all together.

How can I install the SDK's into one xCode so I can build for all different OS versions?

Thanks

EDIT::

Ok so I know I can set the base SDK in xcode, but the options I have are only 3.2 or 4.0, I cant seem to install the 3.1 or earlier SDK's how can this be done?

Final Edit::

Ok got it solved, basically you only need to have an older version of xcode installed to get earlier simulators running, otherwise the articles given to me in my answers as well as others were very helpful:

http://www.clarkcox.com/blog/2009/06/23/sdks-and-deployment-targets/

http://stackoverflow.com/questions/3161385

http://stackoverflow.com/questions/3027120

http://cocoawithlove.com/2010/07/tips-tricks-for-conditional-ios3-ios32.html (possibly the best one)

Answer 1

I tried the same thing some time ago, and it seems some minor SDK versions are automatically removed during the install process...

You may tried to copy them before installing the other XCode versions, and re-install them just after.
They are located in /Library/Platforms/iPhoneOS.platform/Developer/SDKs/ and /Library/Platforms/iPhoneSimulator.platform/Developer/SDKs/.

Note that you can also choose to install each XCode version in a separate directory.
You will lose a lot of hard disk space, and you'll have multiple versions of XCode, each one with different SDK versions.

Answer 2

Is there any particular reason you need to do this? Are you trying to develop applications that will run on iOS 4.x and older versions (3.x)? You can still develop applications which will run on iOS 3.1.x with the iOS 4.x sdk.

Take a look at the following article: http://www.clarkcox.com/blog/2009/06/23/sdks-and-deployment-targets/