Warning: DO NOT upgrade to OS 5.3.1!

Note: most of this post was copied over from Cemetech, it was originally written by PT_ here.

About 4 days ago, TI released a new OS for both the TI-83 Premium CE and TI-84 Plus CE. But as people at TI-Planet discovered pretty soon, it has 2 main disadvantages:

Going into exam mode can now take up 1.5 - 2 minutes, due to the OS checking and validating all the installed apps. Previously this took about 2 seconds.
The [mono]Asm84CEPrgm[/mono] is now permanently disabled, which means you can't write assembmly programs on-calc anymore. Luckily asm programs in general aren't blocked. AFAIK, this isn't a mistake:
Quote from: AdriwebNo it's not a mistake, they confirmed it after all with TI-Dallas. And they say it's only half disabled because they didn't want to block/remove it entirely either, so to use it they say to write and transfer things from TI-Connect CE. But that's also why I (or anybody else, I guess) say it's completely absurd/illogical.

From the community-experience, TI barely listens to our complains, so don't get your hopes up that this will be 'fixed' soon. Personally I've no idea what the future will bring us, but if you have boot code >= 5.1.5 (check with [MODE] [ALPHA] ), don't upgrade your OS. If your boot code is from before 5.1.5, you can downgrade the OS to even OS 5.0.0.

Source:
https://tiplanet.org/forum/viewtopic.php?f=41&t=21187

Thanks to TheMachine02 you can now downgrade from this OS!

Quote from: TheMachine02 on March 22, 2018, 10:16:13 PM
The first tool to be able to downgrade is now out https://tiplanet.org/forum/archives_voir.php?id=1398736