During normal operation, heads in HDDs fly above the data recorded on the disks. Modern HDDs prevent power interruptions or other malfunctions from landing its heads in the data zone by either physically moving ("parking") the heads to a special "landing zone" on the platters that is not used for data storage, or by physically locking the heads in a suspended ("unloaded") position raised off the platters. Some early PC HDDs did not park the heads automatically when power was prematurely disconnected and the heads would land on data. In some other early units the user would run a program to manually park the heads.