They don’t align radially anymore – but the reader doesn’t care. They are not real holes in the disc anymore, but the reader doesn’t care. So that’s what Datel did: they copied an existing BCA, measured the “marks”, and just wrote a bitstream that makes the reader see the marks at the right places. It’s basically “just” writing a sector with very custom data. But because now it’s part of the data, it’s trivial to align them to the right place relative to the rest of the data. Instead, you can just embed them into the bitstream, and basically write data to the disc that looks _very very similar_ to a cut mark – similar enough to fool the reader. Because you don’t _have_ to put the marks on the disc by burning them with a laser after the disc production.
But you have to hit the bits at the exact right position (again, sub-micrometer precision) – wow, that’s hard. Instead, you could attempt to just copy an existing (signed) BCA, and put the marks at the same position as the donor disc. Now if you have all the same equipment that Nintendo has, you could build a DVD, add marks, measure the marks, write a BCA – but you could not _sign_ the data, as there’s a private key required.(***), so you couldn’t produce a BCA that matches your marks. (The Gamecube also does more steps which are generally not well researched.) The Gamecube then reads the BCA, decodes the information where the marks should be, seeks to the indicated sector, measures the distance of the sector header to the beginning of the defect, and verifies that it’s in the expected place. Nintendo takes these measurements, signs(**) them, and writes a BCA with that data. Nintendo then identifies a few sectors that are corrupted, and measures the distance from the sector header to the cut (and width) in bits, i.e. Each disc has the marks at a slightly different position.
Those “marks” will corrupt ~50 bits for each track that they cross. Nintendo masters a regular(*) DVD, produces them, and then destroys a few sectors by using a high-powered laser to cut 6 radial “marks” in ~equal angles, right outside to the BCA (Burst Cutting Area roughly ~188 bytes of information). Posted in Nintendo Hacks Tagged Action replay, datel, gamecube Post navigation That’s exactly what did with his GameCube setup, you can check out the video below. Not that it really mattered, anyway modchips existed, and with the SD to Memory Card adapter you could run homebrew works without having to burn a disc. But surprisingly, this technique wasn’t popularized with the GameCube homebrew scene. It’s a brilliant technique that allows consumer equipment to create the Action Replay disc. Since the BCA is written over data that is already there, you can just encode whatever data the BCA should hold into the raw data of the pits and lands. Why not? The BCA effectively writes over the pits and lands in the first blocks of data in a DVD. Additionally, this BCA can only be cut with a YAG laser that’s significantly more powerful than the laser diode in a DVD writer.īut the Action Replay disc from Datel didn’t have this BCA. This burst cutting area (BCA) is unique to every copy that comes off a single master. On (nearly) every DVD, and almost every GameCube disc, there’s a ‘barcode’ of sorts on the inside of the optical tracks. The Nintendo GameCube disc format is almost, but not quite, the same as a DVD format.
In a fascinating video, takes us around the disc to see how this disc protection scheme actually worked, and how to exploit it to load homebrew games from an SD card. Not only that, but in a decade and a half since the Action Replay came to market, no one has managed to copy their methods. Datel, a British company that produced the Action Replay, the ‘Game Genie of the GameCube’ figured out how to get around the GameCube’s disc protection. You couldn’t burn GameCube games, at least without advanced soldering skills. Around the time the GameCube hit shelves, your basic home computer started getting DVD burners, and you could walk into Circuit City and buy those tiny little DVD-Rs. In theory games could be cheaper (yeah, right), and would hold more textures, pictures, and video. Gone were the cartridges that were absurdly expensive to manufacture. The Nintendo GameCube was the first console from Big N with disc-based media.