The ribosomes are classified on the basis of sedimentation coefficient in the centrifuge. It is measured as Svedberg unit (S). On the basis of sedimentation coefficient they are 70S and 80S.70S ribosome (having larger 50S and smaller 30S subunits) are present in prokaryotes. 80S ribosome (having larger 60S and smaller 40S subunits) are present in eukaryotes.