I just started working on this.
The PB4 SD card can be cloned with no problem. Unline the Game Elf the PB's have no unique serial number nonsense. You can interchange SD cards between machines without alternation to the original image. I mentioned my PB3 dying eariler when my 4 arrived, really the SD just blanked itself for whatever reason. I'm in the process of downloading an image of the PB3 SD from a fellow member here to raise it from the dead.
The PB3 has a wad of hot glue on the end of the card holding it in place. The 4 doesn't have anything like that.
Interesting part: a 4 SD loads and fires up on a 3, but doesn't work properly. CRT video is scrambled & VGA video appears but is shifted to the right with all kinds of weird aspects ratios going on. When you pick a game from the menu it goes to the loading screen, plays it's little loading song, then freezes at the loading screen. Purely speaking out of my ass I assume this is an issue with the way the PB 4 displays CRT/VGA versus a 3. If you hook VGA up to a 4 with CRT simultaneously, you get scrambled video on the CRT, same scrambling as being displayed here when CRT *only*. On a 3 if you hook them both up at once you get video on both outputs, although the VGA will have aspect ratio issues on vertical games.
If the file structure of both cards are the same, it might be as simple as copying over new files on a PB3 card; but the developers went farther out of their way to obfuscate what is going on than they did with a Game Elf.
The next question is would a simpler matter be the King of Air SD card work in a PB4 with no alterations? I'm sure the hardware on those are much closer to a 4 than a 3, especially if they're VGA only.
I guess the file '3a' in partition 1 is the signature file, it's generated with the cpuid of a13
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