PS3 blu-ray drive differences?

[krisztoforo]

Does anyone know if the blu-ray drive used in the earlier (60, 20GB) models is different than the one in new 40GB model?
I assume the specs need to be the same to keep the gaming, etc experience the same, but the actual hardware?
The reason I'm asking is because my copy of the Sorcerer's Stone blu-ray disk won't play in my 40GB unit (the drive just starts clicking periodically and refuses to detect the disk, but all my other movies play fine), and when I put it in an old 60GB model it still takes a lot of time to load (I can hear the drive spinning up and down multiple times), but eventually it does load and start fine.