Still, there's no full support for iOS 4 since weak references only work on iOS 5. Quoting the Transitioning to ARC Release Notes directly from Apple:
ARC is supported in Xcode 4.2 for Mac OS X v10.6 and v10.7 (64-bit
applications) and for iOS 4 and iOS 5. Weak references are not
supported in Mac OS X v10.6 and iOS 4.
From what I can gather yes - ARC is done by the compiler and should be thought of as a wizard or helper that checks all of your code and inserts the correct retain and release statements for you.
This will therefore be compatible with older iOS runtimes.
It will support iOS 4 but not iOS 3.
Still, there's no full support for iOS 4 since weak references only work on iOS 5. Quoting the Transitioning to ARC Release Notes directly from Apple:
From what I can gather yes - ARC is done by the compiler and should be thought of as a wizard or helper that checks all of your code and inserts the correct retain and release statements for you.
This will therefore be compatible with older iOS runtimes.
Edit:
IT will support 4.x but not 3.x