This section describes the physical structure of hard disks and floppy disks, and presents an overview of ways to logically organize areas on your disks.
Both hard disks and floppy disks work similar to an old-fashioned record player, with the record turning on the turntable and a needle playing the music. They are also similar to VCRs and stereo cassettes in that disks, cassette players, and VCRs all use a read/write head to access the information that is stored on the magnetic media.
Hard or fixed disks store information on a revolving platter of metal or glass coated with a magnetic material. The disk typically consists of several physical platters on a common spindle. This platter is similar to the record on a record player, except information is usually stored on both sides of a disk platter.
As the disk rotates, a transducer element called the head reads or writes binary data on the magnetic media. There are many methods for encoding data on the disk, such as modified frequency modulation (MFM) and run length limited (RLL). The disk controller logic determines the method used and the density of data on the disk.
Some high-end disks have as many as one head per track. Therefore, no time is lost physically moving the heads to a track in order to read information. These disks are more expensive and are normally found only on minicomputers or mainframes.
Current state-of-the-art disks do not have platters and heads, but use nonvolatile RAM (NVRAM) instead. The controller microcode organizes the memory into logical cylinders, heads, tracks, and sectors to provide a consistent interface to the operating system. Access times for these disks are measured in nanoseconds rather than the milliseconds for more conventional disks.