PsNee is a designer specifically to bypass the protection system of regions engraved in discs, and the protections in the bios.
Originally PsNee was only designed for the protection engraved on the discs. This protection was based on two specific elements. The first being a specific area of the CDs that is normally used for the calibration of the lasers, on which Sony has implemented a bit of binary code representing the different regions. The second is a specific instruction set, the control unit of the player sends to the laser controller, to go read the specific area. Very quickly the engines realized that it was possible to trick the controller of the player by sending instruction packs on the line between the controller of the player and the controller of the laser. The old modchip followed the evolution of this protection, first by sending without much regard the region code, then by adding specific clocks, to delay the sending.