Playstation games cost upwards of 50$CDN, while CD-Rs cost less than one dollar each. An obvious question is why wouldn't someone just burn copies of their favorite games, and avoid paying the high retail price. The first reason is that this is illegal. The second is that it is morally wrong. The third is Sony's ingenious copy protection scheme to differentiate burned discs from "real" ones. It is this third reason that this entry is concerned with.
The Playstation copy protection works by reading the checksum values of the first few blocks of the disc. Real Playstation discs have a checksum value of zero on the first few blocks. Authorized Sony disc producers have "special" disc writers that ensure the checksum is correct. One may ask "ok, so why can't we write zero-checksums on a burned disc?" The answer is that on a typical home CD-R burner, the checksum data is determined at write-time by the burner itself, and not by the computer. Also there is no combination of data that will produce the required zero-checksum.
"So how about we start booting a real Playstation game and then swap in the copy after a few seconds?" This strategy actually did work for early series Playstations, but also involved modifying the Playstation's disc reader cover so that it could be open without letting the console know. Other "swaptricks" required the use of game cheat devices such as the Action Replay or the GameShark. In any case, this hole was quickly patched by Sony in later series models.
The solution to the burned game dilemma came in the form of the mod chip. This device was a programmed PIC chip that would intercept signals on the mainboard that claimed the CD was a burn, and insert required "this CD is real" signals. The PIC code was altered several times, and ultimately stabilized in the version known as "Stealth Mod 2". This chip is connected to the playstation mainboard with no less than seven wires, and the wires go all over the board. Some of the wires connect directly to pins of chips on the playstation board. Installation is not easy, and can result in a permanently fried console. Correct installation allows the gamer to play his burned games.
Playstation 2s use a similar method of copy protection. Mod chip development is underway but is advancing slowly. A beta-version chip called the Neo 2 functions for some games, but requires 30 wires to connect, and still requires the use of a game cheat device described above. However, a new form of the swaptrick functions for the Playstation 2. This method, discovered by Zima, simply uses a manual override of the PS2 tray motor to prevent the system from reading the first sectors of a burned game.