RedSn0w version 0.9.12b1 introduced two different ways to install the Rocky-Racoon jailbreak on A4 and earlier devices. It could either allow for a backup and restore method, as seen with jailbreak software like Absinthe, or it could use a limeRa1n-based ramdisk approach which doesn’t require a potentially lengthy backup procedure. The latest update improves access to this choice of features.
The problem is that the option to choose an approach wasn’t an accessible in RedSn0w’s GUI itself. The mechanism for choosing an install method was whether or not your device was in DFU mode or not before being hooked up to RedSn0w. If it’s in DFU mode, it uses the limeRa1n ramdisk install; if not, it uses the backup and restore method.
The old selection method needed to be replaced because it requires users to know what jailbreak method they want before they even boot up RedSn0w. RTFM may be good wisdom but explicit options are good GUI.
If f you have a lot of media on your device it could take a while and use up your computer’s hard drive space. If you have a lot of pictures and music on your device, use the limeRa1n ramdisk method.
Unfortunately, the ramdisk method does not support A5 devices, like the iPhone 4S or the second and third generation iPads. These later devices are currently not compatible with the limera1n exploit.
Download RedSn0w 0.9.12b2 - OS X
Download RedSn0w 0.9.12b2 Windows — run in Administrator Mode
If it's hard for you to choose which tool to jailbreak your device, here is a comprehensive analysis.