How Is Data Stored and Retrieved?

Computers record data on hard disks as a series of binary bits. Each bit is stored as a magnetic charge (positive or negative) on the oxide coating of a disk platter.

When a computer saves data, it sends the data to the hard disk as a series of bits. As the disk receives the bits, it uses the read/write heads to magnetically record or "write" the bits on the platters. Data bits are not necessarily stored in succession; for example, the data in one file may be written to several different areas on different platters.

When the computer requests data stored on the disk, the platters rotate and the read/write heads move back and forth to the specified data areas. The read/write heads read the data by determining the magnetic field of each bit, positive or negative, and then relay that information back to the computer.

The read/write heads can access any area of the platters at any time, allowing data to be accessed randomly (rather than sequentially, as with a magnetic tape). Because hard disks are capable of random access, they can typically access any data within a few thousandths of a second.