disk(7)                          UNIX System V                          disk(7)


NAME
      disk - random access bulk storage medium

DESCRIPTION
      The secondary storage devices used by the system are fixed disks and
      diskettes.  Disks are high-speed rotating magnetic media, which are
      treated as a collection of concentric rings, known as tracks.  There are
      several platters (whose number is represented by n) in the fixed disk
      providing up to two surfaces per platter (or a total of up to 2n
      surfaces); each set of up to 2n parallel tracks on these surfaces is
      considered as a group, known as a cylinder.  Each track is divided into
      several sectors.  A sector is usually the smallest unit which can be
      transferred to or from the disk.  However, the drivers allow read or
      write operations of any size to or from any location on the disk, except
      for raw disks.

   Logical Disks
      It is often useful to partition fixed physical disks into smaller
      sections, each of which can hold a separate file system.  The disk device
      driver can therefore divide a physical disk into smaller logical disks or
      partitions.  Each of these logical sub-disks behaves as if it were a
      distinct disk.  A typical division of a disk into logical sub-disks might
      be as follows:

            /dev/dsk/0s0 represents the entire disk on drive 0
            /dev/dsk/0s1 represents the first partition on drive 0
            /dev/dsk/0s2 represents the second partition on drive 0
            /dev/dsk/1s0 represents the entire disk on drive 1
            /dev/dsk/1s1 represents the first partition on drive 1
            /dev/dsk/1s2 represents the second partition on drive 1

      and similarly for the raw (character) logical disks, /dev/rdsk/0s0,
      /dev/rdsk/0s1, etc.

      In fact, more complex arrangements are often created.  It is often
      desirable to have logical disks of different sizes, which are suited to
      different uses.  Similarly, it is often desirable to have several
      alternative ways of partitioning a single disk.  Refer to install (1M)
      and mkpart (1M) for the details of partitioning of a disk.  Instructions
      for partitioning are described in the Operations/System Administration
      Guide.

SEE ALSO
      fdisk(1M), install(1M), mkpart(1M), fd(7), hd(7), intro(7).










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