What Is A Partition?

As you can probably guess by breaking down the word partition, it's a 'part' or section of the hard disk, although that's a bit misleading because 'part' tends to indicate that a partition is less than 100% of the drive. Although a partition 'can' be less than 100% of the space available on a drive it doesn't have to be less. As a matter of fact a hard drive can exist perfectly well on a system without any partition(s) on it whatsoever; it just won't be of any value for accessing and storing data. I think it's a bit more accurate to look at partitions as defining a certain area or amount of space on a hard drive, be it 1 or 100% of the drives total capacity.

Partition Types

Depending on type of system and what operating system is being used there are many different types of partitions, but since this site deals with XP it's most likely you'll be dealing with two types of partitions; Primary and Extended. Depending on who you ask, some people consider logical drives as another type of partition. To me, this is more a case of semantics than anything else, but I've included Logical Drives in this section.
Primary Partition - A partition that is used to start an operating system, although you can use primary partitions that don't contain the operating system. Look at the color coded key at the bottom of Fig. 01 and you'll see that Primary partitions are denoted by the dark blue color.

• There can be up to a maximum of four primary partitions on a single basic disk.
• The Primary partitions do not have to come before Extended partitions as shown on Disk 0.
• A drive is not required to have any Primary partitions as shown by Disk 1
• CD-ROM 1, while it does contain a blank CD, is not shown as containing a partition because there is no data contained on the CD.

Fig. 01

Extended Partition - A partition that can be sub-divided into logical drives. Look at the color coded key at the bottom of Fig. 01 and you'll see that Extended partitions are denoted by the dark green color.

• An extended partition is not formatted or assigned a drive letter.
• It's essentially a container for logical drives that are formatted and assigned drive letters. Disk 0 and 1 contain extended partitions that have a green band surrounding the logical drives (discussed below) that have been created in the extended partition.

Logical Drive - A logical drive is created within an extended partition. Look at the color coded key at the bottom of Fig. 01 and you'll see that Logical drives are denoted by the lighter, bright blue color.

• An "unlimited" number of logical drives may be created in an extended partition, formatted and assigned drive letters. Unlimited is another misleading term used in conjunction with logical drives. The reality is you're limited by the number of available drive letters and the amount of hard drive space available for creating drives. In Fig. 01, Disk 1  has two logical drives, F and G,  identified by the bright blue color and contained within the extended partition. More Logical drives could be created in the Free Space until you either ran out of drive letters or the Free Space was exhausted.
• Disk 1 and 2 also contain Unallocated space that isn't assigned to either a primary or extended partition. I'll deal with unallocated space later in the article.

System and Boot Partitions

This seems like as good a time as any for a brief discussion of System and Boot partitions. In almost every case where I've attempted to explain the difference between System and Boot partitions people have walked away shaking their heads because it just doesn't make any sense, but I'll give it another try. Here we go;

• Whenever a computer system is started, either from a cold boot using the power switch or a warm boot such as restarting the system from within Windows, there are certain files needed to boot (start) the computer. These boot files reside on the System partition.
• Once the boot files have been accessed and performed their function, the system files (the files that comprise the XP operating system) are accessed to complete the system start. The system files reside on the Boot partition.

If you just accept these two statements are true then everything will be fine. I know it makes no sense and seems to defy logic, but it's true.

The boot files reside on the System partition     ---   The system files reside on the Boot partition

Fig. 02

Look at Fig. 02 and you'll see C: is designated as the System partition. There is no designated Boot partition. In most cases this is the standard setup and there won't be a separate Boot partition designated.

Look at Fig. 03 and you'll see C: is designated as the System partition and I: is designated as the Boot partition. The boot files are located on partition C: and the system files (the XP operating system) are installed on the I partition.

Both screen captures are of the identical system so why does one have the Boot partition uniquely identified? The answer is because there are two operating systems installed on the same machine, or what is often called a dual boot setup. WindowsXP is installed on drive C: and Windows XP is also installed on drive I:. When the system is set to boot from the operating system installed on partition C: the system and boot files reside in the same partition so there is no need for a separate Boot partition designation. When the system is set to boot from the operating system installed on partition I: the system and boot files reside on different partitions so partition I is designated as the Boot partition.

Fig. 03

There is one more term that you may occasionally run across and that's Active partition. Any primary partition that has an operating system installed on it may be designated as the Active partition simply for the sake of convenience in making it the System partition. Active partition and System partition mean the same thing.