I'm weighing whether to get a Pentium 4 or Celeron server. What's the difference between the two? Isn't it just the L1 or L2 cache or something?

If you get a celeron just get more ram and it should perform well.

Most of the advantages of Pentium chips relate to sound and graphics, things that your web server is not likely to encounter. Therefore, Celeron is usually the better chip for a web server because it's cheaper and you don't lose to much.

The problem is that Celeron is Intel's secondary line of chips, so the blazingly fastest chip of the moment will always be a Pentium. That's where Pentiums step up to the plate. If you really need a good processor, you're going to want a Pentium.

I have P3, P4 and Celeron. My comment is, Celeron is not bad too. Just make sure your Celeron box have big RAM!

For most web serving needs, RAM is key. Performance bottlenecks are often related to RAM, disk and cpu in that order for most web sites.

Now you may have cgi's or php/mysql apps that hit the cpu pretty good but todays cpus are very fast and unless the scripts are poorly written or have flaws the cpu should not be a factor.

You would actually have to run the test but a celeron server with 1GB of ram would probably out perform a pentium server with 512 MB of RAM on apache benchmark tests.