Access arm
Alternatively referred to as read/write head arm, head arm, or actuator arm. The access arm is in every mechanical computer hard disk drives and is similar to the arm of a record player. As the platter spins the access arm moves the read/write heads to the location information needs to be read, written, or deleted. Below is a picture of what the inside of a hard disk drive and access arm looks like.
Also see: Hard disk drive definitions, Voice coil