iOS4 SDK target to iOS3 device

In previous version of iOS SDK, if I install a newer version of SDK, I can't target a previous version. For example, when I installed SDK 3, i can't target iOS 2 or before.

Now I want to install a new version (xcode_4.0.2_and_ios_sdk_4.3.dmg) to develop to iOS 3.2 and iOS 4.

If I install开发者_开发问答 this new version, can I target to previous iOS 3?

You can specify deployment target in your project's properties. For example if you choose iOS 3.0 as deployment target the app will run on iOS 3 even if it is built with SDK 4.0 (of course it's true only if you don't use 4.0 specific features).

No. Install at Different location so that, if you want to develop applications supporting lower version you can use that older version SDK. However you can change Base SDK version of older version developed apps and can run applications on Newer version Xcode SDK.