Doser grinders have an extra cylindrical chamber in front where all the ground coffee enters. You then pull a lever to dose out the coffee into your portafilter. When making espresso you want to grind coffee as fresh as possible. Ground coffee sitting or the extra process of dosing is not desirable. This is why see more doserless grinders in our store than doser grinders. We even converted a Mazzer Doser grinder to a doserless version.