[ChuckMcM]

The question comes up a lot when you're building very large scale applications. When does it make sense to have your own infrastructure vs using someone else's (like Amazon's).

If you're running 'one' thing (like say a hadoop farm) and you can optimize out the things you don't need, there can be a pretty durable benefit in building your own machines.

People like Rackable, HP, Dell, or IBM who sell servers need to build them able to do 'anything' you might want, in order to do that cost effectively they often put things on the mother board (lowest marginal cost) which are perhaps not useful in all cases. However, when you're using lots of machines you have to power and cool those unused sound chips and USB hub chips, and may firewire ports that aren't really all that useful to a web app.

I talk about it as 'rack level' blades, basically motherboards on a cookie sheet that only have network and storage interfaces. Taking away a size constraint makes building them a lot easier (you don't need a custom backplane for example, you just plug cables in)