Cog-swap is an ELF program which allows it's user to fool the PlayStation 2's copy-protection code. The PS2 checks a loaded disk at boot-time to see if it is an authentic, "pressed", disk with a valid Table of Contents and such. Cog-swap work by loading the validation information from an authentic disk, then freezing the process to load a burned backup disk.
yes, you need a chip for every game that you download or if your ps2 is PAL you can use cogswap. And if you want to play a NTsc and your PS2 , and your PS2 is a PAL version, or vica-versa, you will have to modify your PS2.