Dual-booting is an oft-used solution in the desktop realm, where users value the capability to boot multiple versions of an operating system from the same volume (e.g. Windows Vista and XP, Mac OS X Tiger and Leopard, Mac OS X and Windows on Intel-based Macs). Now a similar solution has been released for the iPhone, allowing users to boot multiple iPhone OS versions (e.g. 1.1.1 and 1.1.4) from the same device. This capability may come in handy when a future, SDK-compliant iPhone OS release (2.0) is released and users with to maintain compatibility with old "jailbreak" applications while taking advantage of enhancements in the new release.
Detailed by Jonathan "NerveGas" Zdziarski, the process is quite involved and requires some command line work. Zdziarksi writes:
"I'll walk you through a sample jailbreak scenario with 1.1.4, using 1.1.1, to show you what I mean. To do this, you will carve out a new partition on the iPhone and install version 1.1.1 on it. You'll then upgrade the iPhone to v1.1.4, which will leave the new partition intact. You can then dual-boot the iPhone, allowing you to mount 1.1.4's partition using the 1.1.1 partition."