How does iPhone jailbreaking work?

I know HOW to jailbreak an iPhone and I also know that jailbreaking uses 'exploits' to get access to the 'root' user which allows apps to run all manner of code that would otherwise not run, but what actually happens? For example:

Is code first run which is known to make the iPhone crash?

Does the crash make Unix fall over?

Is Unix such an insecure operating system that it allows the app to then run any code presented to it?

I find it hard to believe that any 'crash' can't just be simply trapped by Unix and avoid running injected software.

Even in the old days of BASIC, you'd just say ON ERROR GOTO 1000 and any error would force the programme to jump to line 1000 of the code! Nothing could be 'injected'!

I'm intrigued to know!

To my understanding of Jailbreaks on Iphones via a closed Unix system (unixware) and Root on Androids via an open source Unix (linux) system… The crashing that sometimes, if at all, happens on the device has to deal mostly with the bootloaders inconjuction with the kernel.

In Androids, the bootloader is bypassed/masked and the kernel is rooted, thus allowing superuser rights.

In Iphone, due to the closed system nature, and not open source like Android, the bootloader can't be bypassed or masked. Instead, the Bootloader is down graded to a lower version, which can be hacked (IE: iphone 4s running a Iphone 3G bootloader) Thus giving root superuser access to the Kernel. Since this is a vertical privilege escalation, the kernel may have conficts with the "downgraded bootloader", thus causing the crash. OR, if this is a app crash, the app is either coded incorrectly or poorly, OR, again--there is a conflict in the kernel and bootloader--such as the app may be requesting priveledges that the kernel performs but the lower bootloader still denies. OR… The kernel wasn't fully rooted, thus crashing the "jailbroken app" (iphone)/"rooted app" (android). Normally on both devices, This happens easily if settings on 1 app/system causes conflict with another app's settings.

mind you… BASIC was an open source program. Like Linux, it allowed you to do whatever you wanted, given you knew the code. It allowed you to GOTO line xxxxxxxxxxx if given errors. With Android, if there's an app issue/crash, on unrooted or rooted phones, a popup will be displayed asking if you want to send the developers a crash report. The stack of code in question will then be sent to the Dev to determine if its a app issue or "user error".

The Unix Kernel just wants to make you happy regardless if its Iphone or Android… But if coding interferes with priveledges via the kernel/bootloader/both or if root wasn't fully achieved, then your'll get crashes and errors…

but that is just my take on it all… I may be wrong. But the logic works for me so far in my hacking life. LOL