Backward Compatibility
Nearly all PlayStation games can be played on a PlayStation 2 console. PS2 uses hardware-based backward compatibility--it contains the chipset necessary to play PS1 games. This differs from the software-based backward compatibility of newer systems like the Xbox 360--you must download a program to emulate the Xbox. In a software-based approach, each game requires its own emulation profile to run. Microsoft has released emulation profiles for only about half of the games released for the original Xbox.
Function
To play a PlayStation game on the PlayStation 2, turn the PS2 on and insert the PS1 game disc into the disc tray. Close the disc tray, and the game will start automatically. You can plug either a PS1 or PS2 controller into the system to control the game--the game will recognize a PS2 controller as a DualShock, and all button and rumble functions will work accordingly.
Memory Cards
To save your PS1 game data on a PS2 system, you must insert a PS1 memory card into the console. You cannot save PS1 game files on a PS2 memory card. To delete or copy files from a PS1 memory card, insert the card into one of the two memory-card slots on the front of the PS2 console and turn the system on. Select "Browser" from the main menu. Select the PS1 memory-card icon, and you will see a list of your save files. From here, you can delete a file or copy one to another memory card.
Games
Though most PS1 games function perfectly on a PS2, a few don't work well on the newer system. Users who play Final Fantasy Anthology may experience graphical errors, while Mortal Kombat Trilogy and Fighter Maker do not function on a PS2 console at all. Consult an official list of incompatible PS1 games before you attempt to play one on the PS2.
Slimline
The original PS2 model has more functional backward compatibility than the updated Slimline model, which contains a different chipset. Many popular PS1 games--including Driver, One, Lunar 2 and Syphon Filter 2--do not work on the Slimline PS2. If you have a Slimline, consult a list of incompatible PS1 games.