There are several types of server racks, depending on the presence or absence of doors, rails, front and back doors, and side panels, among other features.
Open frame racks have two or four rails for installing equipment. They have no doors or side structure. They are also known as four-post racks and their use is very popular for data centers, thanks to their configuration which allows a better arrangement of cabling and power sources.
A two-post rack only has two vertical columns made of metal, usually aluminum, which can be attached to the floor or the roof. This kind of rack is mostly used in places where earthquake protection is needed.
Server cabinets, on the other side, include keys, rails, doors and protective panels on the side. Sometimes these protective panels are isolated with foam layers for specific uses.
Also, there are racks with wheels, for those cases where mobility is needed. Some racks that can be mounted in walls, a good solution for locations with limited space.