Prokaryotic ribosomes are called 70S ribosomes and have physical dimensions of approximately 14 to 15 nm by 20 nm, and are made of 50S and 30S subunits. The S stands for Svedberg unit in the measurement of ribosome sedimentation coefficient unit. This is a calculation of the velocity of sedimentation in a centrifuge; the faster a particle travels when centrifuged, the higher its Svedberg value or the coefficient of sedimentation. The coefficient of sedimentation is a task of the molecular weight, volume and shape of a particle.Their cellular arrangement differs significantly from that of eukaryotes, which is made up of nucleoid-containing, membrane-bounded organelles, of which there are frequently numerous per cell.