Why is the Hard Drive the C: Drive?

You guys may have wondered, why do we have C drive? Don’t the English alphabets start with A? Shouldn’t we be having A as the first drive letter, the drive for installing the Windows OS? If this is what you have wondered, rest assured, we are going to tell you why is the hard drive the C: drive?

Reason for drive letters in Windows

This nomenclature or the assignment of drive letters is done so that the storage devices could be easily identified and would also be user-friendly to use. Due to drive letters we the users and the OS can perform required actions in a more simpler way.

Why C Drive?

The Windows systems follow a pattern while assigning letters to its storage devices. Have you ever noticed, that it assigns the first available drive letter to the first connected storage devices? Well, it really does that. You’ll see that the virtual drives after C would be D, E, F, and G serially. This is because these alphabets appear one by one after the letter C. Now to the question, why C? Well, you already know it. Because, A and B, the previous drive letters are reserved for other types of storage devices, hence are not available. Shocking, right? Because if this is the case, then how come we don’t find the A and B drives? Why can’t we use these storage devices? Well, because they aren’t there in the first place.

What about A and B?

Turns out, the A and B drive letters, we are talking about are reserved for floppies. This is because long before when hard drives were not so common, the primary storage devices were the floppies. Moreover, when one floppy wasn’t enough for storage purpose, people began to use two floppies.

Hence, not one but two of the drive letters, A and B were reserved for the primary storage devices, the floppies. Later when hard drives had just begun to spread, they had to use C letter because A and B were reserved for floppies. Now, the new Windows operating systems still follow the same convention and have still kept A and B reserved for floppy disks.

The algorithm

MS-DOS and PC DOS version 5.0 and higher use the following algorithm to assign drive letters:

  1. The first floppy disk drive, (drive 0) is assigned letter A. The second floppy disk drive, (drive 1) is assigned the letter B. In case there’s only one floppy installed, B will be assigned to the same first floppy disk and will be mapped into A. If no floppy disk is installed, there won’t be any drive letter assigned but A and B are reserved. If more than 2 floppies are installed, higher letters will be assigned.
  2. Assign C to the first active primary partition, so that boot drive will be either A or C.
  3. Assign subsequent letters to first unassigned primary partitions.
  4. Assign subsequent letters to every valid logical partition present in the first extended partition.
  5. Assign letters to all remaining primary partitions subsequently through physical hard disk drives.
  6. Assign drive letters to all remaining physical floppy drives.
  7. Assign subsequently, drive letters to block device drivers in CONFIG.SYS via Device statements, e.g. Ramdisks.
  8. Assign subsequent drive letters to any dynamically connected drives using CONFIG.SYS INSTALL statements, in AUTOEXEC.BAT or later. Here, additional optic disc drives, PCMCIA/ PC card drives, USB or Network drives are assigned.

Note: Hidden partitions are not assigned any drive letter. So don’t think that the system reserved and recovery partitions are assigned A and B letters.

Vishwesh Thonte

I'm a computer engineering student, fascinated by the complexity of zeros and ones, more fascinated by laws of physics and even more by intelligence and cognition. I'm normally reserved but not with special ones.

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