Forum .LRN Q&A: Re: AOL performace data
Mark, you need a much more detailed idea about what it is you're application is trying to do. (And you didn't even mention disk IO, which for an RDBMS can be the limiting factor.) As Jun pointed out, serving 100 requests per second could be nearly trivial, or very difficult, it all depends on what those requests are doing. You posted this in the .LRN forum so perhaps you intend to run .LRN?
Modern CPUs, RAM, disks, and networks are so fast that many interesting sites can be run with quite modest hardware. But even much fancier hardware isn't all that expensive nowadays. For more towards the large high-volume end of things, see the Denis Roy's Jan. and Feb. posts with details on the hardware they use for aiesec.net.
I may be a bit out of date, but currently I'd guess that a rather high-end dual SMP system might have two 3+ GHz Intel Xeons (or AMD Athlon MPs or Opterons of similar or better performance), 8+ GB ECC RAM of commensurate speed, and depending on use, 4-12 or more fast disks in a RAID array (more disks is better). I'm not sure what that machine would cost currently but you're not talking tens of thousands of dollars here. Maybe there are some OpenACS sites out there big and complicated enough that a monster dual CPU box like that would be just too wimpy to run the RDBMS, but if there are I haven't personally heard of any of them.
Most sites probably never need hardware anywhere near that. (For example, openacs.org certainly runs on much more modest hardware!) And anyway, if you think you need more than that, my guess is you're probably either Yahoo or AOL or some big corporate entity like that with a massive public website, or (more likely) you have egregiously poorly performing software and just throwing more hardware at it probably isn't a good idea anyway.
Hardware gets faster all the time, but the design of your software is still, and probably always will be, the dominant factor in meeting your performance goals for a large and complex site. If nothing else, Jim Davidson's Feb. 2000 slides on the AOL Digital City site architecture should help show that.