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PCs For Dummies Quick Reference, 4th Edition

Demystifying Disk Drive Letters on a PC


Adapted From: PCs For Dummies Quick Reference, 4th Edition

Disk drives in your PC are assigned famous letters of the alphabet, starting with A and moving on from there. This historical thing with PCs dates back to the first PC, which lacked a hard drive. That explains why the drive letter assignment isn't exactly logical.

The first three drive letters are the same for all PCs:

  • Drive A: Drive A is reserved for the PC's floppy drive, even if your PC doesn't have a floppy drive.
  • Drive B: Drive B isn't used on modern PCs. Originally, it was assigned to the PC's second floppy drive.
  • Drive C: Drive C is the first hard drive. This is the PC's main hard drive, the one on which the operating system (Windows) is usually found.

Beyond drive C, there are no rules regarding which drive is given which letter. This situation causes some confusion in that many users mistakenly believe that drive D is always the CD-ROM drive. That's not true.

The PC's startup program assigns drive letters D and up to any disk storage devices found beyond the first hard drive. Priority is given to any additional hard drives. So, if your PC has two hard drives, the second one is drive D.

After hard drives, the next priority is given to internal disk drives, such as CD-ROMs or perhaps a Zip drive. Those drives receive the next letter in the alphabet after the hard drives are assigned letters.

Finally, removable disk drives are given drive letters in the order in which the computer finds those drives.

Network drives can be manually added to your computer system at any time. When the drive is added, you're allowed to choose a drive letter based on whatever letters are left.

The highest letter allowed for any disk drive on your PC is drive letter Z.

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