On: Alex Gaynor - Thoughts on HipHop PHP

[ehsanul]

That's interesting. I'm sure some people here, like me, believe the opposite, since I/O is so much slower than processors now. Can you give a bit more of an explanation as to what kind of applications are CPU bound and why?

[wmf → ehsanul]

I/O is slow if you actually do any, but RAM is so cheap that many Web sites shouldn't need much I/O.

[nixy → wmf]

I think that by I/O in this case people mean network I/O, not disk I/O.

Edit: Sorry, maybe I was jumping to conclusions. Databases and files are of course not always cached in-memory.

[ericb → ehsanul]

What wmf said sums it up. In terms of who is CPU bound, it often points to a need for caching or indexing. All it really takes to be CPU bound is to use up more CPU than your hardware can offer. Once you are CPU bound, you're unlikely to push traffic through fast enough to be network or disk I/O bound. If you're caught on something else, like CPU, the speed of those things won't matter much.