it seems jim is right about memory and disks

http://blog.topix.net/archives/000011.html

"Wade smacked me on the head (gently) and asked why I
was even thinking about disk anymore. Disk is dead;
just put the whole thing in RAM and forget about it,
he said.

Orkut is wicked fast; Friendster isn't. How do you
reliably make a scalable web service wicked fast?
Easy: the whole thing has to be in memory, and user
requests must never wait for disk.

A disk head seek is about 9ms, and the human
perceptual threshold for what seems "instant" is
around 50ms. So if you have just one head seek per
user request, you can support at most 5 hits/second on
that server before users start to notice latency. If
you have a typical filesystem with a little database
on top, you may be up to 3+ seeks per hit already.
Forget caching; caching helps the second user, and
doesn't work on systems with a "long tail" of zillions
of seldom-accessed queries, like search.

It doesn't help that a lot of the scheduling
algorithms found in standard OS and database software
were developed when memory was scarce, and so are
stingy about their use of it.

The hugely scalable AIM service stores everything in
memory across a distributed cluster, with the
relational database stuck off to the side, relegated
to making backups of what's live in memory. Another
example is Google itself; the full index is stored in
memory. Servers mmap their state when they boot; no
disk is involved in user requests after everything has
been paged in."

__________________________________
Do you Yahoo!?
Yahoo! Small Business $15K Web Design Giveaway
http://promotions.yahoo.com/design_giveaway/