The first PS3 units (20 and 60 gigs) had both the PS2 CPU and GPU that are Emotion Engine and Graphics Synthesizer. I don't know whether they were unified or not. Those first units weren't released to the European market. But later on, with the release of 80 GB units Sony discarded the EE but kept the GS. Those units play fewer PS2 games than the original. Finally when there were a lot of PS3 games, PS2 compatibility completely went away when Sony launched first 40 and 160 GB parties with DualShock 3 support.