When Playstation reads a disc, it looks for a special sequence on the disc that tells the Playstation "hey, this is a Playstation game. You should load it."
That sequence is proprietary and isn't on burned copies of games. This is anti-piracy protection, and makes sense from a monetary standpoint.
When you put Alien: Resurrection in the console, which has that sequence, the Playstation is told that "hey, this is a real Playstation game. You should load it." The game loads, then you can put in the cheat, which tells the game to stop loading from the disc momentarily while another disc is loaded (think "please insert disc 2 from final fantasy"). At this point, you can pop in your burned copy of the game, then press a button to continue loading from disc, at which point the game tells the system "hey, this new guy is with me. Let him through", and the Playstation loads the new game from the disc.
Importantly and how it's different to FF is that it boots the content without calling the disk reset and if you keep the disk button wedged then that reset never triggers, so that copy protection isn't called, where as FF basically triggers a drive reset which is why you couldn't use that.
i don’t really know, but an educated guess is that it has to do with how old the console is, and how micro optimized/hacky things had to be at the time. for example, morrowind would reboot your xbox during loading screens. there was probably quite a lot more control given to developers in the olden days, whereas now things are more sandboxed. but i would be happy to be corrected on anything i’ve said here.
“There’s been great tricks that [Xbox] taught us,” Howard said. “My favorite one in Morrowind is, if you’re running low on memory, you can reboot the original Xbox and the user can’t tell. You can throw, like, a screen up. When Morrowind loads sometimes, you get a very long load. That’s us rebooting the Xbox. That was like a hail Mary.”
That's interesting but that's still in that one game. This thing sounds like it allows you to play burned roms forever afterwards, which means it really affects the system itself.
As I understand it, it has lax checks if all disks are original. Some games required many, Pt.1 was on one, Pt.2 was on another, and a memory card sewed this monstrosity together whenever you switch disks - as it had no HDD, no install options.
Designing a game around that was hard and probably meant frequent checks, delays, and also a player having incomplete game if only one disk is missing or scratched if they want to play again - and you swapped them back and forth. So that dev implemented zero-check on a second disc after the first one is checked, a command to kill a game and start anew, and with that you can put whatever you burnt on your CD, leaving the console clueless it's not your actual disk 2. It still needs you to boot with original Aliens first and put code, so it's not exactly stealing anything directly, but oh god it's an interesting vulnerability.
I haven't heard of something akin to that, besides weird cartridge combos on old consoles where you put one into another or other heresy like plug-in cartridge readers, hardware extenders, etc. It seems Sony was convinced the first check is there, and it's ok, but never thought you can abuse it up that great, and had no further investigation was put.
For a console that aged, that had hardware jailbreaks and emulators for years, I don't feel they'd hurt him now. Twenty years is too much even for them. They'd still sell mini-PS1 without any problem as it has no disk reading capabilities and won't care.
The PS disc copy protection is only checked when the system is booted. You can load one legit disc and swap it live for a burned disc, but it's difficult because the disc is spinning the whole time.
This cheat code on a legit disc just stops the disc from spinning for a short time, allowing you to much more easily swap to the copy.