Let's see if I understand this right: you want to determine how powerful your server(s) need to be before starting to write your program?

If I had to make such a decision, I'd probably ask myself the following questions:

1. What features does the program need? Heavy database applications can require lots of RAM/CPU.
2. How many users do you expect to serve? Do you want to create a second Slashdot?
3. What's the penalty for not serving your customers fast enough? Are they willing to wait, or is your application so mission-critical that you must acknowledge the request within a specified amount of time?

Based upon these (and perhaps more?) questions, I could deside what amount of servers I would need. Or at least, I could take this into account when designing my application!

Those few applications I've developed didn't require more than one server to give a reasonable response-time...

Hope this helps! Greets,

-- JaWi

"A chicken is an egg's way of producing more eggs."