LC-Asia: Facebook contemplates ARM servers

Well, let's say there's about 100MB of system software. With the price of DDR3 at around $6/GB (http://www.dramexchange.com/), that makes it of the order 60 cents per CPU unit.

Fixing the issue to reduce system software overhead would probably cost 4 person-years; or about $1M of burdened payroll.

That makes payback at around 2 million CPU units. Feasible, but probably not cost effective. And by the time the redesign is finished, DRAM prices will have dropped again.