Chances are at some point you have pulled up the screen that shows your hard drives and all of the other connected devices. You have also probably noticed that your computer’s main hard drive is labeled as C, but yet there is no A or B. Why is that exactly?

It Wasn’t Always This Way

How to differentiate between the different storage and input devices that connected to a computer was one of the early problems that had to be overcome in the computing world. In the 1960s IBM developed a system to differentiate different local drives using letters. The system that we know today was born, at least in a primitive form. The idea was copied by early software pioneer, Digital Research, who then used them as designations for local storage devices.

In the early 1980s IBM developed the first true personal computers. Which operating system would be used would be a lucrative contract for that company that could make or break it. Digital Research seemed to have the inside track with their CP/M 86 Disk Operating System (DOS) with IBM and Digital Research reaching a handshake agreement when allegedly the founders of Digital Research (who were serendipitously on the way to a vacation) and a representative of IBM spoke while on an airplane.

Enter Microsoft

Talks broke down somehow between IBM and Digital Research and apparently no clear indication of why has ever been put forth. Digital Research claims it was because the founder’s wife refused to sign a non-disclosure agreement while her husband was out of town on business and later that IBM did not honor their agreement. IBM claims that none of that ever happened.

What is clear is that IBM shifted their focus to another software company, Microsoft. Microsoft purchased a clone of Digital Research’s operating system and modified it calling it MS-DOS. Included with that clone was the disk drive lettering system that we know today. Microsoft of course flourished becoming one of the world’s most valuable companies. Digital Research was sold off in 1991 when their version of DOS failed to gain market traction.

A And B

A local disk reader was not a new thing for a computer. They dated back to the 1950s, but because there was no local storage there was no need to differentiate it from other devices. Hard drives were expensive and even early personal computers lacked a hard drive or had a very small one. Over time though that began to change.

Since early personal computers used disks to run programs the initial disk format, the 5 ¼” disk was given the designation A. When the next generation of disks, the 3 ½”, were developed they were given the designation B. While not always the case with every computer, this format won out. It was easy to remember and easy to accept as the universal standard.


Over time physical storage on a personal computer became cheaper and more compact. By the late 1980s the hard disk drive was becoming common in personal computers and that drive was given the next letter in line, C. C has come to be known as the drive that contains the computer’s operating system.

Since then there have been many, many further innovations. Multiple hard drives, CD, DVD and Blu-Ray drives, external hard drives, network drives and any other storage devices that can be plugged in are given their own letter. Even digital cameras or your smartphone. Despite the floppy drives that were A and B going the way of the dodo bird the hard drive with the operating system has retained the letter C as its designation.

The Drive Letters Are Not Set In Stone

Did you know that these drive letters are not set in stone? You can change them, so if you want your hard drive to be A, you can do that. You will have to change a lot of other things around as well, so don’t do this unless you know what you are doing, but these drive letters are not set in stone. You have the entire alphabet to work with.

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