Re: why is AE on a PC so much faster then a Mac ?

After Effects is not a 64 bit application on any platform.
AE CS4 provides some of the benefits associated with 64 bits apps (also in the Mac OS), because of how the multiprocessing scheme allows to take advantage of far more than 4 GB of RAM by launching a rendering instance for each core or processor (each able to use up to 3.5 to 4 GB).

I work for Adobe, so I don't need to predict :) Unfortunately, I can't tell you, since there are no announced plans about this. But, evidently, Adobe seems to be talking a lot about 64 bit, right?

Finally, while there can be some rendering advantages for certain features in one or the other platform, I'd consider drastic differences (> 20 per cent) very, very rare.

Adolfo Rozenfeld · Adobe