Understanding Hard Disk Partitions
Table of Contents
-
- Why make partitions
What is a hard disk partition
When a hard drive is installed in a computer, it must be partitioned before
you can format and use it. Partitioning a drive is when you divide the total
storage of a drive into different pieces. These pieces are called partitions.
Once a partition is created, it can then be formatted so that it can be used
on a computer. When partitions are made, you specify the total amount of storage
that you would like to allocate to that partition from the total size of the
drive. For example, if you have an 80 GB drive, then it would be possible to
make one partition consisting of the entire 80 GB of available storage. Alternatively,
you could make two partitions consisting of a 20 GB partition that will be
used for the operating system and programs and a 60 GB partition set aside
for data,
music, and images.
In the current IBM PC architecture, there is a partition table in the
drive's Master Boot Record (section of the hard dirve that contains the commands
necessary to start the operating system), or MBR, that lists information about
the partitions on the hard drive. This partition table is then further split
into 4 partition table entries,
with each
entries
corresponding
to a partition. Due to this it is only possible to have four partitions. These
4 partitions are typically known as primary partitions. To
overcome this restriction, system developers decided to add a new type of
partition
called the extended partition. By replacing one of the four
primary partitions with an extended partition, you can then make an additional
24 logical partitions within the extended one. The table below
illustrates this.
Partition Table |
| Primary Partition #1 |
| Primary Partition #2 |
| Primary Partition #3 |
| Primary Partition #4 (Extended
Partition) |
| |
Logical Partition #1 |
| |
Logical Partition #1 |
As you can see, this partition table is broken up into 4 primary partitions.
The fourth partition, though, has been flagged as an extended partition. This
allows us to make more logical partitions under that extended partition and
therefore bypassing the 4 partition limit.
Each hard drive also has one of its possible 4 partitions flagged as an active
partition. The active partition is a special flag assigned to only
one partition on a hard drive that the Master Boot Record (MBR) uses to
boot your computer into an operating system. As only one partition may be set
as the active partition, you may be wondering how people can have multiple
operating
systems installed on different partitions, and yet still be able to use them
all. This is accomplished by installing a boot loader in the active partition.
When the computer starts, it will read the MBR and determine the partition
that is flagged as active. This partition is the one that contains the boot
loader. When the operating system boots off of this partition the boot loader
will start and allow you
to choose which operating
systems
you would like to boot
from.
Why make partitions
Now that you know what a partition is, you may be wondering why you would
even need to make multiple partitions instead of just making one. Though there
are quite a few reasons, we will touch on some of the more important ones below:
- Multiple Filesystems - When you create a partition, you
then need to format it before it can be used. When formatting a partition
you tell the operating system what filesystem you would like that partition
to be formatted in. Once you format a partition, and therefore assign the
type of filesystem you want to use with it, you can not change that filesystem
without formatting the partition again and losing all the data contained
on
it. If you require different filesystems on your computer, whether it be
for security or for a specific application, you can then make multiple partition
and assign one type of filesystem to one of the partitions and another to
one of the other partitions.
- Partition Size - On older operating systems the maximum
size of a partition was limited. Therefore if you had more storage space
on a
hard
drive than was usable in a single partition, you would need to create other
partitions to utilize this unused space.
- Multiple Operating Systems - Some operating systems use
filesystems that are not compatible with other operating systems. If you want
to use two operating systems on the same computer that are not compatible
in this way, you could then make two partitions, one for each operating system.
Then a boot loader could be used to switch between them when you start your
computer.
- Wasted disk Space - When a filesystems store data in
a partition, the larger the partition, the greater the chance of wasted
space.
By having multiple partitions of smaller size, you reduce the amount of
waste
that filesystems may create.
- Seperate system files from users files - Some components
of an operating system require storage space to operate. For example, in
Windows
if you have no hard drive space available on the drive that Windows is installed
on, you will not be able to print. By creating a partition solely devoted
to the operating system and then another partition dedicated to your own
data and programs, there is less of a chance of you using up the space on
the operating
system partition with your data, and thus not causing problems.
--
Lawrence Abrams
Bleeping Computer: Hardware
Tutorial
BleepingComputer.com:
Computer Help & Tutorials for the beginning computer user.
Have a problem and would like to ask us for help? To learn how to ask your question Click Here!
Do you have popups or other malware infecting your computer? If so, Start Here!
Are you having trouble using this site? Then you should visit the New User Orientation Center!
