how high speed is called ultracentrifugation? - (Jul/24/2014 )

How high speed of centrifugation is called ultracentrifugation? And what is the speed range of ultracentrifugation?

This is a tricky one but probably any speed above what you would find in a standard centrifuge, which would usually be around 20-30,000 rpm.

and they top out at ~100,000 rpm (sorvall) or ~90,000 rpm (beckman).

perhaps you can define it from the function, i.e. centrifugation speeds that are capable to separate/sediment organelles and other cell components and (macro-)molecules...