Number of 5.25" bays
A drive bay is a standard-area for adding hardware to a computer. Most drive bays are fixed to the inside of a case, but some can be removed. A 5.25" drive bay, also known as full-height bays, were found in old PCs in the early to mid-1980s. They were 3¼″ high by 5¾″ wide, and up to 8″ deep (83 × 146 × 200 mm), used mainly for hard disks and floppy disk drives.