Do you mean separate databases for the fact and dimension tables?

I am curious to know if this slows down joins between fact and dimension tables due to their being in separate DBs.

It would also be possible to use separate disks (RAM disks?) for different parts of the DW (staging tables or lookup tables as well as dimensions or facts or even indices) but remaining within the same database.

Is your advantage in having separate servers for each part of the DW?