A hard drive is the primary data storage of computers composed of several layers of highly polished magnetic discs spaced within a few millimeters apart. Modern hard drives has the same basic storage structure of early vinyl discs and the same recording element of a magnetic tape. Hard drives use an actuator arm to locate data across the surface of the platter and uses a copper wire head. Copper heads are used because they are easy to magnetize and demagnetize quickly. The copper head floats just a few millimeters from the platter and held by an arm. The actuator basically uses electric actuators based on Faraday's law of induction. Data storage on a hard drive is arranged in a circular pattern called tracks and divided by a series of sectors.
The data is stored on a hard drive through small magnetic impulses that are read by the "read" copper head and then sent to the CPU for binary conversion composed of ones and zeroes. The binary data would be decoded by the CPU and other hardware components, the computer's onboard programs down to the specialized software created to convert a particular data based on a series of rules that will eventually turn the binary data into a designated format whether it is for videos, images or texts readable by humans.
A data request is done the opposite way, from the human interface down to the software which converts all instructions to binary data to the CPU and converts it back to magnetic impulses and instructions that will spin the platter and actuate the arm to the exact location of the data within a couple of milliseconds. A data re-write involves the destruction of data on a sector where the file is located and the uses a write head to copy and replace the same data with a few or significant instruction changes.
Major hard drive manufacturers
Seagate Technology (NASDAQ : STX
Western Digital Corporation (NYSE: WDC
Fujitsu (TYO: 6702
Samsung (OTC: SSNLF.PK
NEC Corporation (TYO: 6701
Toshiba (TYO: 6502
Hitachi (TYO: 6501