So I'd like to discussion things to do with old mobile computing gear...such as iPads, iPhones, iPod Touch, Android Phones and Tablets (or even PDAs, Ultramobile PCs. Netbooks like Chromebooks)... Chances are you have one or two of these collecting dust somewhere in your home.
I recently become re-interested in my 7th Gen iPad which came with the first gen iPencil, at the same time I was given a hand-me-down iPad 5th gen that was no longer needed by previous owner (my wife)... Neither of these had been used for a while and (FORTUNATELY) had NOT been updated, I was (somewhat intentionally) most guilty of that. Its an iPad 7th gen that has iPad 13.4.something which is getting stale (its Safari/Webkit is old), but my wife had auto-updating turned on. The last time she updated it was 15.6.1, excellent!
Mind you these aren't terribly old devices yet, the iPad 7 came out late 2019, its 5 years old now, but for some who are into the latest-greatest mobile devices I guess they might consider that ancient. Anyway, they're both under-used, like new. And (for now) they're both still getting official updates.
I had already jailbroken my iPad 7 a few years back because I wanted to try out iPad-ports of Mini vMacII and Basilisk II, which is why I never wanted to bother updating the thing unless I knew I could re-jailbreak it on whatever the new version was, the problem is I should have been keeping up with the scene and *saving signature 'Blobs" for each update as they came out, In fact I've barely had time to use this iPad for much for some time now, so I didn't. And now, because iPad 7 is still officially supported for now, my only choice for an update is to go to the latest (and greatest) iPadOS 18 signed update available for my device, which is either 18.1.1 or 18.2 (both are currently being signed by Apple as I write this). This is because Apple revokes the signatures for old versions as soon as new versions come out.
The version I'd REALLY like to get installed on the iPad 7 is the version the iPad 5 has on it, which is 15.6.1. The reason I want that version is because it is the newest version that has a bug which has been exploited to enable of apps to be permanently signed, which while enabled can sign a jailbreaking app, enabling the device to be what is known as a semi-untethered jailbreak. Thereafter the device can jailbreak itself. This exploit is only usuable from iOS 14 - 16.0.1 and then were patched out by Apple...but I have iPadOS 13.4 and can only go directly to iPadOS 18! There's NO legit way to update to say iPadOS 15.x (like I should have while it was current). My iPad 7 (and all of Apple's A11 and below CPUs) has an updatable exploit, I could still connect it to a computer for and install a jailbreak, on 18 but I think it would be semi-tethered, meaning if I reboot the device I'd have to connect it to a computer again to get it back into a jailbroken state. THAT is the reason I wanted to got to 15.x, so it wouldn't ever need to be connected to a computer to be able to enable arbitrary code to run.
Also, there is NO WAY TO DOWNGRADE either, if you find you don't like the 'upgrade'! You can't just re-sign the update and install it. The 'OK good' signature is sent from Apple and it's tied to a your unique device's IDs, and a specific model and specific iOS version. Those are the 'Blobs' that enable an update to be installed and you need them to install an iOS update. So you can only use an update that you have this 'blob' for and you can only get that unique-blob while Apple is still signing that version. Making it nearly impossible to update to any previous intermediate version of the OS for which you do not have this 'blob' saved.
In any case, being able to run the device in a jailbroken (aka Custom Firmware) state has a several advantages (and a few disadvantages) over running stock OS. The ability to run arbitrary code being the main advantage, there's lots of open source software that has been ported by iOS home-brew coders, and even alt-App stores where indy devs sell their software. But there's other reasons too. There are lots of these patches that people have created too, called 'tweaks', that can enable all sorts of things. You can even use it to have the second stage bootloader boot you into Linux
( someone was able to get an early iDevices to boot Android-Arm64). You can run some emulators that are unavailable in the AppStore (despite Apple recently reversing course on it a bit and allowing some emulator software their AppStore). There was also a more capable version of the Emu/VM called UTM (built on QEMU) which could do virtualization of ARM CPUs on Apple's ARM-based CPUs. The version on the AppStore now is called UTM SE is somewhat hobbled. With these can run some actual real Desktop OSes on your iPad with layers of windows and menus and trashcan!
There are many of apps that can work perfectly well on MUCH older iDevices that have long had official support dropped many years ago now and are otherwise not really very useful devices. If an app you want for your iDevice (stuck on an old iOS version) is still on the app-store but there's a newer version now, and you didn't get the older version from the AppStore before that new version came out, you will get a message 'about the iOS version needed' and whatever the new minimum iOS is for the newest version of the app. That means even if there was once a version of this app that was in the AppStore and ran on your version of iOS, you can't get it! That is unless you install and run the old version some other way, such as a jailbreak.
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