Hi! First of all, sorry if my English is not perfect, I'm from France but I'll try to do my best to make this message understandable.
I have recently worked on my first big project (2weeks of work) with After effects CS6, and I had really BIG problems with the Ram Preview.
Basically, the Ram Preview on After Effects CS6, is not reliable at all and has really bogus behavior.
For example when I hit "0" on the numeric pad (to start the rendering of the Ram preview), some times it won't start render, or it will take super long time before starting to calculate frames. Instead if I hit the "space bar" it will start immediately. But with method you're not seen your animation in "real time" and with no sound and it's not what I want to do.
Some times while rendering it won't show you the green progress bar so can't really know how many frames are calculated.
After the the Ram preview is over, and I make a change in let's say frame 150 (that have no effect in previous frames), and even some times without any changes, and want to see my Ram Preview again, the computer will start to render from frame 1 again, loosing all the previous frames that were already calculated before and after the changing frames...
...And there are many other examples...
Working in this conditions is very frustrating, and it requires much more time for the same results.
In order to find solution and searching the net, I tried different settings related to CPU, RAM allocated to each processor and disk cache, but nothing worked.
At the end, I found a solution that works in a way. The "solution" is to deactivate multiprocessing rendering. Then you get a reliable ram preview again but that renders on only one processor so once again you loose a lot of speed.
My computer is IMac, Intel Core i7 @ 2.8GHz, with 16GB of RAM.
So if there's anybody experiencing the same problem, tell me.
And I'd like to know if Adobe is aware of this problem.
Thanks for reading.
Merlin PARDO.