Arm Assembly

The component in the disk drive that reads and writes to the disk platters is referred to as the head.  There are multiple heads, one for each data surface.  For example, if a hard drive has six data surfaces, it will also have six heads.  All the heads essentially do is take electrical impulses coming from other components on the disk drive, and convert them to magnetic impulses that attach to the magnetic material on the platters.  They are the most expensive component on the hard disk drive because they determine how fast and how efficiently the drive can read and write data.  Although there are multiple different heads on a hard drive, only one of these heads can read or write at one time.

Arm Assembly

The heads do not make contact with the platters, but instead float over them on a layer of air.  Head arms that are attached to an actuator suspend the heads over the platter.  The head arm moves the heads over the platters while they spin in order to access data everywhere on the disk.

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