LAMP is the application stack, but it need not all be installed
on the same host. As others have noted for performance, security
or scalability purposes often these are not installed on the
same host. You can also find that hardware which is optimal for
one part of the architecture may not be for another. For
instance, databases are all about storage management. The faster
I can get information off of the disk then the faster I can get
it to the requestor. If I am sharing a disk subsystem with
several other application stack members, such as a web server,
the contention I face on the shared resource of the read and
write heds of the disk drives can actually hinder my
performance. Also, having RAM split between web server and
database server on a given host may not provide a large enough
resource pool for either to run in its most efficient fashion,
able to cache as much information in RAM without having to go to
the disk either for an image, a page, or a query result set.
Administratively there are efficienci