Things You'll Need
Instructions
Purchase a Mini DisplayPort adapter cable that is capable of working with either component video, composite video or HDMI cables. The PlayStation 3 gaming console supports all three of these video cable types, while the 27-inch iMac monitor only supports Mini DisplayPort signals.
Connect the video cables of your PlayStation 3 to the Mini DisplayPort adapter cable you purchased. Connect the other end of the adapter cable to the Mini DisplayPort input on the iMac.
Press the "Command" and "F2" buttons on your iMac keyboard simultaneously. This will switch the unit into a mode called "Target Display" which allows it to be used identically to a regular external computer monitor.
Turn on your PlayStation 3. Video information from your PlayStation 3 will appear on the 27-inch iMac monitor.