Computer hard drives have not changed much since they were first introduced to the home computer market. To retain each bit, these systems make a physical change to the storage medium - they alter the magnetic field. Information can be stored for long periods of time, or erased and re-recorded over as needed. Macintoshes and Intel-styled computers use the same type of hard drive. Hard disks, floppy disks, and tape systems use magnetic storage.
CD drives use optical storage.
PC Cards use solid-state memory. Random access storage On floppy and most hard computer disks as well as some CD and DVD formats, the recorded data are organized to take advantage of the two-dimensional aspect of the flat wide surface to give fast access. Instead of being arranged in a single straight line, disk-based data are spread across several concentric circles similar to the grooves of a record, or the pattern of waves rolling away from a splash. After the head reaches the correct circle, it still must wait for the desired bit of information to cycle around under it. Because the head can jump from byte to byte at widely separated locations on the disk surface and because data can be read and retrieved in any order or at random in the two-dimensional disk system, disk storage systems are often called random access devices.