Look at the serial number. Find the sticker on the back of your PS3. The last digits will inform you as to whether you have full hardware backwards compatibility, or limited software emulation:
CECHAxx (60 GB) and CECHBxx (20 GB) - Full hardware backwards compatibility.
CECHCxx (60 GB) and CECHExx (80 GB) - Limited hardware emulation (These models do not contain the Emotion Engine, as it is instead emulated by the Cell processor). You may run into issues with some PS2 discs.
CECHGxx and above - These models are not backwards compatible.
