Usually when Apple releases the newest version of their iOS, the first Jailbreak solution is a “tethered jailbreak” version, which has caused some confusion as to it’s definition. I’ll explain what a tethered jailbreak is versus an untethered jailbreak, and why one is better than the other. If you want the short answer: an untethered jailbreak is always better.
A quick note: a tethered or untethered jailbreak has nothing to do with internet tethering, which is the process of using your cell phone as a cellular internet modem.
Tethered jailbreaks are frustrating because they require a computer connection to boot a jailbroken iOS device. The concept of a tethered jailbreak has been around a long time, but essentially it means this: every time your iPhone or iPod touch reboots or the battery dies, you have to connect (tether) your iOS device back to your computer so that the hardware can boot with the aid of the jailbreak application.
Using and Booting a Tethered Jailbreak
In the most recent example with redsn0w and iOS 4.2.1, you had to do the following if the jailbroken iOS device is rebooted:
Connect the iOS hardware (iPod, iPad, iPhone) to your computer
Relaunch the same redsn0w application you used to jailbreak the device
Select the “Just boot tethered right now” option (shown in the screenshot above).
The jailbroken hardware will now boot with the aid of redsn0w
After the device has been booted you can then disconnect it from your computer and use it as usual, just remember that if the battery dies or you reboot the iPhone/iPod you will need to connect it again. These tethered jailbreaks work with both Mac OS X and Windows.
An untethered jailbreak is the preferred jailbreak because it requires no connection to your computer except for the initial jailbreaking process. You can reboot your iPhone or iPod touch as much as you want without having to tether it to your computer to boot. If the battery dies on a device that has an untethered jailbreak, it’s no big deal you just charge it again and it will boot as usual. This is how most of the modern jailbreaks work for iOS 4.1 and prior, like greenpois0n, PwnageTool, limera1n, and sn0wbreeze.
Using and Booting an Untethered Jailbreak
There is nothing to it. Boot your iOS hardware as usual, an untethered jailbroken device behaves like any other iPhone, iPod touch, or iPad, you can reboot at will trouble-free.
With iOS 4.2.1 the untethered jailbreak is currently only available for iPhone 3G and older iPhone 3GS models, but the iPhone Dev Team is actively working on untethered solutions for other iOS hardware.
Tethered vs Untethered Jailbreaks
Due to the hassle of tethering (connecting) your iOS hardware to a computer on each boot, an untethered jailbreak is obviously preferred.
If you are patient, I would always recommend waiting for an untethered jailbreak to become available for your hardware. If you are determined to proceed on the cutting edge of jailbreaking, learn how to jailbreak iOS 4.2.1 with redsn0w 0.9.6b4, but as I stated before, the untethered option is only available to older hardware: the iPhone 3G, old iPhone 3GS, and old iPod touch 2G. Most people are better served by waiting for an untethered jailbreak to be released.
iOS 4.3.1 has an untethered Jailbreak available through Redsn0w.
By Carl W. Brooks