Case

A computer case is the enclosure that houses most of the electronic circuitry of a computer. A computer cannot run without a case.

HDD refers to the number of internal drive bays, which can fit both 3.5" Hard Disk Drives (HDDs) and 2.5" Solid-State Drives (SSDs).

OPT refers to the number of external 5.25" drive bays, where optical drives (CD/DVD/BR) can be installed.

FAN refers to the number of case fans that can be installed within the case.