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Logical Drive (back to computer page)

As the price of computer media storage drops and more storage is required, some users may find themselves partitioning a physical hard drive into two or more virtual storage units known as logical drives. Although these virtual drives actually reside on one piece of physical storage equipment, they are put into practical use as a series of smaller, separated disk drives. This article will explore how one physical drive is partitioned into multiple drives, some benefits of using logical drives, a few misconceptions, and some considerations when using such storage areas.

    Function

  1. When a brand new hard drive is delivered from the manufacturer and installed into a computer, the fresh drive is free of any formatting or other user-specific operations. To use the drive, the user must first perform a physical format on the drive (to get it ready for operation), then a logical format (to prepare it for use in the intended operating environment and to support the correct file structures). When the logical formatting is performed, the disk may be divided up into several logical drives, areas of the disk that are logically separated by data the computer reads as separate disk drives. When the user's computer--or computers on a network--connect to the drive, the logical formatting causes them to see it as a series of storage devices instead of one solid hard drive. While data stored on the drive is physically stored on the same devices, computers that see the drive as several logical divisions can only access the logical drives with which they are associated.
  2. Benefits

  3. The logical drive division of computer storage helps serve a variety of purposes. Users who do not want to mix data--separating personal files from sensitive business data, for example--can use each logical drive separately, almost like two distinct computing environments. Users who want to use two separate operating systems (OS), such as Microsoft Windows and Linux or Macintosh OS X, can install an OS on each logical drive in order to keep the incompatible file types separated. In addition, multiple network users can connect to their own distinct logical drive, keeping their individual data separate and protected from all other users (except the network administrator).
  4. Size

  5. Logical drives can be created in virtually any imaginable size. Although they are of no practical use today, logical drives have been created in sizes as small as one megabyte. The typical logical drive in today's computing environment may be as small as one hundred megabytes (100MB), but the default logical drive size used in IBM system configurations is around two gigabytes (2GB). According to IBM, the current maximum size for a logical drive is around two terabytes (2TB).
  6. Identification

  7. How a logical drive is identified to a user's computer depends on how that computer is accessing the drive. In a typical home setup where one Windows computer may be accessing many logical drives, the drive identification is assigned by the order in which the drive is mapped (the first hard drive is typically assigned a letter of C, the next drive is designated D, the next E, and so forth). Macintosh and Linux/UNIX users may identify the drive by assigning a human-readable name to it such as "My Hard Drive," "My Second Drive," "My Friends Drive." In a business, thin client, or large network environment where the user only accesses a single logical drive, this drive is generally viewed by the network client as the only storage drive available and is treated as if it were a lone drive installed in the machine (though UNIX or Macintosh network users may see the name assigned to the drive by the network administrator).
  8. Considerations

  9. Logical drives can be quite useful in home, network, or business applications. They are not, however, without their caveats. Since logical drives are simply logical partitions on a single physical storage device, any issue which affects the physical device also affects all logical drives residing on that device. In a power outage, multiple users may experience a loss of service when the physical drive becomes unavailable. In the event of a natural disaster, fire, or other catastrophic loss of a physical device with multiple logical drives, the loss of data can be equivalent to losing multiple hard drives. Finally, hard drive crashes that typically affect only one user can create widespread loss of data if multiple users rely on that drive for their logical storage.
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. Windows XP 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.

 

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