A head may refer to any of the following:
3. A read/write head or RW head is a device found on the arm of a hard drive that is used to read and write data from the hard drive's disk platter. Hard drives usually have one read/write head for each platter side. While idle, each head resides on the platter, and when the platter spins, an air cushion develops causing the head floats 3 to 20-millionths of an inch above the platter. When data needs to be read or written, the read/write arm is controlled by a motor in the actuator. Below is an example of the inside of a desktop and laptop hard disk drive.
A hard drive is a magnetic media and works by using the write head to polarize sections of the hard drive to face North (up) or (down) to represent either 1 or 0 (binary). Once the information is written to the hard drive, it is read by the read head that detects the polarization of each section of the drive to understand the data.
In the picture above, the write head has already written "10100101" to the hard drive and has four more visible empty places. To write information (change the polarization), the electromagnetic write head changes the wire coils electric current direction. One direction makes the North face up, and the other direction causes it to face down.