How to Partition a Hard Drive or SSD on Windows and Mac

An essential step in preparing a storage medium, partitioning has advantages for separating the system from the data on a computer. Here’s what you need to know about partitioning a hard drive or SSD.

Even if you are not aware of it, all the storage media that you use on a daily basis on your computer (hard disks, SSD, USB keys, memory cards) are partitioned. Without this indispensable operation, there would be no formatting, and therefore no storage! It is indeed thanks to partitioning that one creates "volumes" – or "drives" according to the terminology of the operating system used – which are used to preserve data (files or folders) durably. But since partitioning and formatting are usually done at the factory, by the manufacturer of the disk, SSD, key or computer, these preparatory technical operations remain practically invisible to the average user who is content to browse the volumes at his disposal to save or read files. The notion of partitioning is even so transparent that many are unaware that the disks installed as standard in their PC or Mac host "invisible" partitions intended for the operating system (Windows or macOS). Let’s emphasize that the principle of partitioning is independent of the operating system : it is common to Windows, macOS and all Linux distributions. The purpose of this practical information sheet is precisely to clarify the issue.

What is a partition ?

As its name suggests, a partition is a "part" of a storage medium: it is also sometimes referred to as a "section" or "region", or even as a "logical" unit, as opposed to a "physical" unit, which corresponds to the hardware medium, i.e. the medium itself. Thus, a hard disk or an SSD can be virtually "cut up" into several parts or into a single part, depending on usage and needs. These parts, or partitions, are independent from the point of view of the operating system – and therefore of the user – even if they are physically located on the same medium. Hence the famous distinction between logical and physical units. To take an image, it’s like dividing a space – a place like a warehouse, a house or an apartment – into several rooms separated by partitions. Everything is stored in the same physical space, but in different areas.

In the case of a Windows PC, for example, a 1TB disk or SSD can be perfectly divided into three partitions: one of 500GB, one of 300GB and one of 200GB (the numbers are deliberately rounded off to simplify the point). Each partition then behaves like an independent disk from the other two, even if they are all located on a single disk or SSD. Each one is displayed with its own volume or drive letter (:C, :D, :E or other). But one can as well decide to use it "in one piece", with a single partition taking advantage of all the physically available storage space (i.e. 1TB in our example).

However, it is not enough to partition a storage medium for its partitions to be usable. Because once created, they still need to be formatted by assigning them a file system: FAT32, exFAT, NTFS, ext4, etc. It is only after this formatting that the partitions become usable to write and read data. Note that the choice of a file system is made for each partition independently of the others. It is quite possible, on the same disk, to have a partition in exFAT, another in NTFS and another in ext4, for example. It all depends on the intended use of each partition. To learn more about this very rich subject, consult our practical sheet.

Finally, it should be noted that, regardless of their format, not all partitions have the same status. Some, known as the main or primary partitions, are intended to accommodate an operating system, while others have more general or more specific uses. Moreover, some partitions are visible and usable "normally", via Windows Explorer or the Finder of macOS, for example, while others are invisible, or at least hidden, because they are reserved for the operating system – but they can be accessed in particular cases or with dedicated tools.Thus, when Windows 10 is installed on the disk of a PC, the system automatically creates four partitions:a visible main partition System, for Window; a hidden partition EFI (EFI System Partition or ESP) which contains files intended for the UEFI, the firmware which manages the motherboard and the basic functions of the computera hidden Microsoft Reserved Partition (MSR); and a hidden Windows Recovery Environnment (WinRE) which is used to troubleshoot the PC in case of a big problem.

Why partitioning a disk ?

But what is the point of dividing a storage space into several parts? Isn’t it easier and more convenient to use a disk or SSD in "one piece" ? Well, no! It is useful and even essential to divide certain disks into several parts, in particular in the case of disks intended to accommodate an operating system. It is not by chance if Windows and macOS automatically partition the disks on which one installs them, without asking anything, for their own needs !

Because the interest of partitioning is precisely to separate data to put them in independent sections, and even "étanches". Partitioning is thus compulsory when you want to use several operating systems on the same computer with a single disk (Windows and Linux, Windows and macOS, or even different versions of Windows). But even when using a single system, it is strongly advised to partition the main disk of a computer. The idea is simple: partitioning separates the operating system from personal files. The advantage of this "logical" separation is that in the event of a major problem, the system partition can be completely emptied and even reformatted without affecting the personal data stored on the other partition. This is not always feasible when everything is on the same partition. That’s why experts always prefer to split the system and data on different partitions (called SYSTEM and DATA, for example), when they have only one disk, even if it’s large. The clean reinstallation of a system is then at the same time simpler, faster and safer.

In the case of secondary disks, which do not contain an operating system, and in particular external disks, partitioning is not essential. But it is not prohibited either, for example to separate volumes according to their contents, to dedicate a unit to automatic backup, or to use different file systems, at the time of formatting, and thus to ensure a compatibility with several devices or operating systems.

How to partition a disk on Windows

With a Windows PC, there are several ways to partition a storage medium (hard disk or SSD) and, more generally, to manage partitions (create, resize, delete). As these operations are quite technical – and therefore delicate, not to say dangerous – they are not performed directly in Windows Explorer, but with specific tools.

  • The first and simplest tool is the Windows Disk Management tool, which can be accessed by right-clicking on the Start menu. It offers many functions with a clear graphic presentation, menus, dialog boxes, etc. To learn more about the possible manipulations, see our practical sheet.
  • The second, much more complex, is the DiskPart utility from Microsoft. Much more powerful, it can perform more sophisticated and delicate operations, even on disks that Windows does not recognize. But it is austere because everything is done in an old-fashioned interface, in text mode, using commands to be typed… To know everything about this tool, consult our practical sheet.
  • The third solution consists in turning to specialized utilities which are not proposed by Microsoft but by third party editors. There are many of them, some free, such as EaseUS Partition Master Free, AOMEI Partition Assistant Standard, Partition Manager, Active Partition Manager or Partition Wizard Home Edition, and others with a charge, such as Partition Find & Mount, Paragon Partition Manager or O&O Partition Manager Pro.

Whatever solution you choose, you must be aware that partitioning is a sensitive operation that is intended for "experienced" users.

How to partition a disk on Mac ?

On the Mac, everything that concerns formatting and partitioning is done with a tool that comes free with macOS, the well-named Disk Utility, which can be used with internal media (hard disk or SSD) as well as external storage devices. As is often the case with Apple software, the interface remains user-friendly even for fairly complex operations. To learn more about this tool and its functions, check out our handy sheet. In addition, as with Windows, it is possible to use third-party software from specialized publishers, such as Hard Disk Manager for Mac from Paragon or iPartition from Coriolis System.