Disks - 1960s to 1990s

Historically the disks, known a Count Key Data (CKD) were dismountable and looked like curling stones externally, although internally they were a stack of disks on a central spindle, with all bar the outer two having recording surfaces on each side of the disk.

Data recording was on a series of concentric rings, known as tracks, with all tracks in vertical alignment being known as a cylinder.

In the 1970s, IBM introduced a different disk architecture known as Fixed Block Architecture (FBA), where data was recorded in 4K chunks, which made them similar to the recording segments on a PCs disk.

However not all of IBMs Operating Systems supported FBA devices.