Performance Tuning, hardware-wise

I wonder why there is no mention at all in the documentation about hardware considerations
- aside from CPU and Memory stuff, which is probably a) _way_ to obvious (a faster CPU
will always make everything faster) and b) too bound up with both fincancials and also
this vast zoo that we have, of different brands and architectures, which is a minefield of
potential flamewars - what I mean is simple, straightforward stuff such as disk layout?!

I just stuck a 2nd hard drive into a box that will serve as a web/database server and it
seems glaringly obvious to me also (maybe that's the reason why there is no mention of
it?!), that that is a good idea. Because: If the same physical disk that contains the root
of the webserver also houses the PGDATA directory, then a call to a web page that is
enhanced with stuff from the database will have the disk almost simultaneously try to
access the static file and retrieve (a) row(s) from some table which is physically located
someplace elso on the disk. What with hard disks being the slowest devices in any computer
(aside from, of course, tape, floppy, cdrom etc.) by orders of magnitude, the plan to have
different drives for database and web root surely seems a good one. I am just wondering
whether this is all mad rambling or decent common sense. I would also be keen to have some
sense of _how_ much I can hope to gain by such measures.

A more extreme idea: If I know that the total size of my database won't grow over, say, a
gigabyte, then why shouldn't I invest my money in RAM (little more than $500 these days,
for a G of RAM), create a ramdisk of 1 G (provided my architecture can house that much RAM
but that's beside the point), and mount /usr/local/pgsql/data right there?!

Am I going mad?

- Frank