1) There are two different "PS2 mode" :
- Hardware : it's only available on earlier FAT PS3 (with 4 USB port on front).
- Software : Sony never unlocked it, but there's a software emulator in the PS3 firmware. This emulator is verrry slow and doesn't work with a lot of games.
The cobra USB Dongle unlock both PS2 mode for ISO launching:
- if you have an old PS3 you can use the PS2 hardware with PS2 ISO
- If you have a non backward Compatible PS3, then you can use the software emulator.
Only Cobra USB allow the launch of PS2 ISO. (maybe a Rebug cfw has that feature too? I didn't follow rebug developement lately).
2)
I don't know about PSP.
I never checked info or tried anything.
3) like he said, there's pretty much no differences except the used term : "Hacked" or "jailbreaked" is the same thing. "Jailbreak" was first used for unlocking phones. So it's also used to tell "I'm unlocking my console to add features".
Though, "Custom Firmware" and "Jailbreak" is not totally the same thing.
A custom firmware is a jailbreak/hack, as it allow you to run new things, unsigned application, homebrew etc.
But a Jailbreak is not always a custom firmware.
Custom firmware implied a completely modified firmware loaded in memory. It can be permanently installed on the PS3 HDD and booted at launch instead of the official firmware, or a "redirected" firmware file loaded at launch of the console, but not stored in the PS3 HDD (loaded through USB, with USB firmware Loader for example).
A hack can also be something that is NOT a custom firmware, not a complete firmware.
For example, the first hacking method of the PS3 was using a USB hub to modify the memory of the PS3 in real time, allowing the console to run unsigned content and homebrew.
There was no modified file from the firmware involved, only a temporary memory (RAM) patch.
The real custom firmware appeared later, by applying these memory modification directly to the files in the firmware, and it then became a modified (custom) firmware.
4)
You can play backups from both internal HDD or external HDD.
Some games have better compatibility with one or the other.
You can check the compatibility list
here.
So, you can have a "low capacity" internal HDD, but remember that most games still have to install on the PS3, like a PC game you run the setup and it install the game on your computer. These "installed data" usually have to be on the internal HDD, so it's always better to have a big HDD to keep all your games at the same time. else you will have to reinstall them each time you want to play another game.
6)
Yes, some Manager (the homebrew "multiMAN" at least, I don't know about other managers), allow you to dump DVD and Bluray movie to internal HDD.
These dump can be mounted to make the PS3 think the folder is actually a real disc reader with this content inserted as a disc.
You can then let your PS3 play it as if it was a real disc.
It's not the homebrew who is playing it, but the PS3 itself.
The homebrew just patch the memory of the PS3 to make it think there's a disc inserted in the drive, that's all.
Attention : It can only read unencrypted DVD & Bluray.
The dump you are doing yourself with the PS3+multiMAN are crypted, you need to put the dump on your computer and use a de-crypter first, then put it back on PS3 internal HDD to play it.
7)
Latest point you didn't ask:
only PS3 with firmware up to 3.55 can be hacked.
If your firmware is 3.56 or more, the only way to hack it is by using a downgrader (hardware material to solder to the console's mother board).
There's a jailbreak/hack in developement for PS3 firmware 4.0, but it will not allow the launch of backup games. Only homebrew games/emulator/mediaplayer/some applications will work.