A computer system module assembly has modular equipment enclosures slidable and securable in a modular exoskeletal frame structure on a base. The frame structure includes horizontal frame members on which the enclosures slide with pawls movable on a threaded rod to engage studs on the enclosures to clamp the enclosure to the frame. Air cooling units in the enclosures provide independent cooling for each enclosure, moving air preferably from front to back of the enclosures, through perforated frame doors.