When a iDevice is booting, it initially loads Apple's own kernel. Each time the device must be exploited and have the kernel patched when it is turned on.
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There is also Semi-Tethered Jailbreak solution, which means that when the device boots up, it will no longer have a patched kernel so it will not be able to run modified code, but it will be usable for normal functions such as texting or making phone calls. To use any other feature that require running modified code then the user must start the device with the help of jailbeaking tool for it to start with the patched kernel.
- Untethered Jailbreak
An Untethered Jailbreak has the property thatis user turns the iDevice off and back on,it will start up completely and the kernel will be patched without using a computer, thus the user can boot without the need of using a computer. These jailbreaks are harder to make and it takes a lot of reverse engineering and many years of experience.
- Tethered Jailbreak
With a Tethered Jailbreak, computer is needed to turn on the device each time it is rebooted. If the device starts on its own then it will no longer have a patched kernel, and may get stuck in a partially started state. By using a computer, the iDevice is essentially re-jailbroken using the boot tethered feature of a jailbreaking tool each time it is turned on. With a tethered jailbreak , we can still restart the SpringBoard (It is the home screen,which is a standard application which manages the iOS home screen) , i.e Respring the device without needing to reboot.
- Semi-Tethered Jailbreak
There is also Semi-Tethered Jailbreak solution, which means that when the device boots up, it will no longer have a patched kernel so it will not be able to run modified code, but it will be usable for normal functions such as texting or making phone calls. To use any other feature that require running modified code then the user must start the device with the help of jailbeaking tool for it to start with the patched kernel.