| When the UNIX operating system was first
developed, hard disks could store what is now considered a very small
amount of data. When disks larger than 300 Mbytes arrived on the
market, the operating system could not address such a large amount of
space. This necessitated the development of logical partitions
of the hard drive to allow the kernel to access smaller, addressable
parts of the drive. Partitions can be either physical or logical. If a
partition takes up the entire physical hard disk then it is a physical
partition. If the hard disk is divided into smaller sections, these are
considered logical partitions.
Today, with hard drives being sold with
up to a Terabyte (Tbyte or a million million bytes) or more of space
on them, the kernel can access all available space. Despite this, the
convention of partitioning a hard drive into logical partitions has
persisted for various reasons. Partitioning allows an administrator to
functionally organize data so that user files are on a different
logical partition than operating system, executables or applications.
One of the main advantages to this is
that daily backups can be done only to those partitions on which the
data changes frequently, without having to back up all information on
the disk. Logical partitioning also cuts down on seek time. If the
disk is partitioned, when a user specifies a file to search for or a
directory to change to, the name of the directory gives the kernel
information about where the information is stored. This prevents the
system from having to seek the information over the entire disk. Other
benefits of partitioning include security and dynamic size allocation.
For increased security, partitions on servers can be shared to the
network or not which means that a system administrator can make them
unavailable for workstations to access when desired. Partitions or
file systems can increase or decrease in size dynamically.
Logical partitions are referred to as file
systems. They are transparent to a user and therefore appear to be
just part of the directory hierarchy. The most common file systems on
a UNIX system are /usr, where binary and executables are
stored, /opt, where third-party applications are usually
located, and root (/), where the files that pertain to the
operation of the system are kept. A UNIX file system is
similar to a drive letter in the PC world or a Volume with Novell
NetWare. Most hard disks in today's PCs are one physical partition
which is referred to as drive C:. A PC hard disk can also be divided
into smaller logical partitions, which are referred to as drive C:,
drive D: and drive E:, etc.
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