One or more racks in a rack computing system include shelving systems with mounting portions to receive computer systems in the mounting portion. The mounting portion can include an air flap structure that can restrict airflow through internal space of the mounting portion when a rack computer system is absent from the mounting portion. The air flap structure can retract to enable a computer system to be mounted in an internal space of the mounting portion. A mounting portion can include at least a portion of a backplane assembly that can be aligned to couple with a rack computer system mounted in the mounting portion to communicatively couple the rack computer system with one or more communication networks. The mounting portion can include an ejection mechanism that can eject an installed computer system from the mounting portion.