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The C drive (C:) is the main hard disk partition which contains the operating system and the related system files. In Windows operating systems, the C drive as represented as “C:\”, the backlash representing the root directory of the drive.
The C drive is considered as the primary hard drive of the system and is used for storing the operating system, system files and other applications and their related files.
In later Windows version, the C: drive is labeled as Primary Drive or Local Disk, and can be accessed by default by opening the “My Computer” folder.
The letter-naming scheme for disk drives dates back to the early days of DOS. The letters A and B were reserved for the floppy disk drives, whereas C was assigned to main hard disk partition which had the operating system and related system files.
Older versions of DOS assigned a letter to each floppy drive before taking hard drives into account. This way, if the computer had more than two floppy drives, the hard disk drive would have been called D:, E: and so on. However, starting with DOS 5.0, drive C: was assigned to the first physical hard disk regardless of the number of floppy drives, to give it boot priority (boot drive was either A: or C:).
Letter A and B were reserved for floppy disk drives since most computer had two different types of floppy drives, one for 3 1⁄2″ floppies (A:) and the other for 5 1⁄4″ floppies (B:).
Other letters (D, E, F, etc.) could be assigned to other hard drives, flash drives, or optical drives (CD drives, DVD drives, Disc Duplicators, Blu-ray drives, etc.). In other words, letters were used for determining logical drives, although much later they were also used for specifying the physical storage devices.
Even today, the computer keeps reserving the A: and B: drives for the floppy disk drive and removable media even if they are not present in most computers anymore.
As the hard disks were smaller compared to today’s, a single letter assignment was all what was needed. Most of the time, the operating system resides on the C drive.
However, today it is possible for the C drive to refer to a smaller portion of the larger disk that also has several other drive letters. The other letters may refer to additional partitions of the same storage disk. This is done to keep the operating system partition protected from infected data, or to ensure better scalability.
In case of hardware or operating system upgrades, the C: partition can be formatted without affecting the data in other partitions. It is also useful to avoid filling the OS partition completely, causing the system to crash or stop working as intended.
The C: partition should always be protected against the most serious cyberthreats. Hackers, viruses and spyware often target the C drive as it is the default drive for installation of the operating system.