Windows 11 usually calls its main volume C:, even on a new PC that has never seen a floppy disk. The missing A: and B: are not a setup error or wasted storage. They are a convention inherited from early personal computers, preserved because changing familiar paths can break software.
A historical explainer by Windows Latest’s Abhijith M B traces that convention through CP/M, MS-DOS, and the IBM PC. For today’s Windows users, the useful lesson goes beyond nostalgia: a drive letter is an access path, not a physical property of an SSD. Understanding that distinction makes storage changes and troubleshooting less confusing.
Why the first hard drive became C:
Drive letters predate Windows. CP/M used letters to identify disks, and DOS carried the idea forward. However, CP/M’s alphabetical scheme did not itself establish the modern association between A:, B:, and floppy drives. That association came with the IBM PC and its DOS environment.
Early PCs relied on floppy disks for their operating system, programs, and documents. The first floppy drive was A:, and a second was B:. When the IBM PC/XT arrived in 1983 with a hard disk, C: became the hard disk’s familiar designation.
There is an interesting wrinkle: a computer did not need two physical floppy drives for B: to have a purpose. As Windows Latest explains using Microsoft’s MS-DOS 2.0 documentation, a single-drive machine could treat two different floppy disks as logical drives A: and B:. Users swapped disks when prompted, allowing operations such as copying a file between them.
That is why simply counting physical drives does not explain the lettering. B: already had an established role even on some machines with only one floppy drive. Hard disks entered an ecosystem whose first two letters were effectively spoken for.
Why Windows still keeps the convention
Modern Windows storage is not fundamentally dependent on an alphabetic name. Its underlying device and volume infrastructure can identify storage independently of the letters shown in File Explorer. Drive letters provide a convenient, widely understood way for users and applications to access it.
The obstacle to changing the default is compatibility. Installers, shortcuts, scripts, configuration files, and older applications may contain assumptions about particular paths. Some use Windows-provided locations correctly; others embed a path beginning with C: directly.
That does not mean Windows can only ever run from C:. It means changing the established access path of an existing installation is not equivalent to changing a cosmetic label. Microsoft’s Disk Management guidance, cited in the source article, warns that changing letters on volumes containing Windows or applications can cause problems locating files or running programs.
For a working PC, there is no practical benefit in trying to make the Windows volume A: merely to restore alphabetical order. Leave its letter alone. This story explains an existing convention, not an announced Windows 11 storage change that requires action.
A drive letter is not a physical disk
The distinction matters when adding or replacing storage. One physical SSD can contain multiple partitions, with more than one accessible volume receiving a letter. Other partitions may have no letter and serve recovery or system purposes. A mapped network location can also appear with a letter despite not being a local disk at all.
Consequently, C: and D: do not necessarily mean “first SSD” and “second SSD.” Before formatting, repartitioning, or replacing anything, check the disk layout, capacity, and volume identity in Disk Management rather than relying on a letter alone.
A missing letter also does not automatically indicate missing data. It can be an access-path issue, but it can have other causes. Do not initialize or format an unfamiliar disk merely because it is absent from File Explorer, especially if it should contain existing files.
Can you use A: or B: today?
On a modern PC without a conflicting assignment, A: and B: can still be used for suitable data volumes or mapped drives. They are not permanently forbidden names.
For an ordinary secondary data volume, Windows provides letter management through Disk Management: right-click the volume and look for Change Drive Letter and Paths. Availability depends on the selected volume and its role. This is not a recommendation to modify Windows, recovery, or other protected partitions.
Before changing a data volume’s letter:
- Back up important files and record the existing assignment.
- Check whether installed applications or scheduled tasks reference it.
- Review backup destinations, library locations, and shortcuts.
- Update dependent paths and test the affected workflows afterward.
Renaming the volume’s visible label is often a better choice if your only goal is easier identification. A descriptive label such as “Photo Archive” improves recognition without requiring you to change its drive-letter path.
Folder mount points offer another option
Windows can also expose a volume through a folder mount point instead of a separate letter. For example, an additional storage volume could be accessible through an appropriately configured empty folder such as C:\Archive.
That arrangement does not merge the two volumes or magically increase the free space available everywhere on C:. Files stored through the mount point reside on the mounted volume. Backup coverage and capacity monitoring still need to account for that underlying storage.
For most home PCs, conventional letters remain the simplest option. For more complex systems, folder mount points can provide a clearer layout. Either way, the guiding principle is the same: choose stable access paths, document what depends on them, and avoid changing them solely for appearance.
Source: Windows Latest’s drive-letter history explainer by Abhijith M B