Disk partitioning, sometimes known as disk slicing, is used to divide a data storage device into multiple sections, or partitions. There are numerous reasons to do this, from simply organizing the files and directories on a large hard drive to running multiple operating systems on a single drive, and some partitions can even be made to span over multiple drives within a single system.

But what exactly is a disk partition? More importantly, how are disk partitions commonly used in modern computing?

Master Boot Record (MBR) & GUID Partition Table (GPT)
Some earlier operating systems (OS), including DOS, Windows, and some iterations of Linux, relied on a master boot record (MBR) to locate your system's OS and load the necessary resources into memory. Due to technical limitations, however, it was eventually replaced by the GUID Partition Table (GPT).

The GPT is compatible with all modern operating systems. It serves a very similar function to the MBR in older configurations. Both use logical block addressing (LBA) to store and retrieve data blocks within a partition or hard drive.

Boot Partition & System Partition
While both of these partitions are critical to the normal functionality of nearly any modern computer, there are conflicting definitions for each one. Generally speaking, the boot partition is generally takes the form of a primary partition that is responsible for storing the system's boot loader. Conversely, the system partition essentially contained the directory and files that are used by your computer's OS.

Microsoft, however, considers the system partition as the preferred means of storing the boot loader. Likewise, their boot partition is used to store the operating system directory and its files.

Primary Partition
In most applications, a primary partition is only necessary on a bootable drive. As such, it contains only one file system. When using a drive strictly for additional data storage, most users would benefit from the simplicity and ease-of-use of an extended partition.

When using the GPT configuration, all partitions are considered primary partitions. Instead of using extended partitions, GPT has virtually no limit on the number of primary partitions and, as a result, extended and logical partitions are rendered moot.

Extended Partition & Logical Partition
Modern HDDs can only contain one extended partition. However, the extended partition can be further split into logical partitions as needed. When this is done in some older operating systems, like early iterations of DOS and Windows, the new logical partitions are automatically assigned a unique drive letter upon creation.

Although it resembles a completely separate drive within the OS, and it's even treated as such in many instances, it's really just a virtualized drive within the physical hard drive's sole extended partition.

Using Partitions to Your Advantage
Partitions can be used for a variety of reasons. In personal computing, partitioning is generally reserved for file organization. Some might use separate partitions to run different operating systems, but this is generally done by advanced users. In an enterprise or multi-user setting, however, partitioning is a great way to maximize system scalability, optimize system performance, and improve data availability.

You may read more about disk partitioning in Wikipedia: Disk partitioning.