A head may refer to any of the following:
3. A read/write head or RW head is a device on the arm of a hard drive. It reads and writes data from the hard drive's disk platter. Hard drives usually have one read/write head for each platter side that resides on the platter while idle. As the platter spins, an air cushion develops making the head float 3 to 20-millionths of an inch above the platter. When data needs to be read or written, the read/write arm is moved and 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 uses magnetic media and works using the write head to polarize sections of the hard drive to face North (up) or (down) to represent either 1 or 0 (binary). When the information is written to the hard drive, it is physically represented as a magnetic polarization on the platter. Later, the head can detect this polarization, reading 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.