Why is (C:) the Default Hard-Drive Letter?

Ever Since the start of the digital era, with the launch of the personal computers, with presumably the MS-DOS, we have seen the default Hard-drive as C: -drive. The question arises as to why?

Back in the 1960s, IBM’s virtual machine operating systems were quite popular. The logic behind assigning different storage devices with simple letters is generally tied to the virtual operating systems, originating from CP-40 and CP/CMS systems. Although, in the initial stages, the letters were used to deal with then logical drives, it gradually came to be associated with physical drives with the beginning of CP/M systems.

Two decades later, when IBM took initiative to use the then relatively popular and widespread CP/M system created by Digital Research, Inc. on its personal computer, they suffered quite the setback. The agreement was a no-go between IBM representatives and Digital Research Inc. for reasons still unknown today. Though there are rumors that they started when Dorothy Kildall, wife of CP/M programmer Gary Kildall, declined to sign the non-disclosure agreement at the starting phase of the negotiations, stating that she would not sign such an agreement without the approval of her husband, who at that time was out of town. This was considered rather unexpected as such matters were mostly handled by Dorothy anyway.

Purportedly, it was Gerry Davis, Digital Research’s attorney who advised her not to go for the deal. As it was, it greatly annoyed IBM representatives and they chose not to go for the deal. Later in the chapter, Gary Kildall stated that IBM didn’t honor their agreement to which, IBM’s representative, Jack Sams furtively denied.

Later, IBM decided to move on from the popular CP/M to instead a deal with Microsoft, and later MS purchased a license to a CP/M clone named 86-DOS. It was then adapted for IBM’s new PC, with quite a few significant changes made to its architecture by Microsoft which named it MS-DOS.

After all, being derived from a CP/M clone, MS-DOS had many features copied along with the drive lettering schema from the original, which had borrowed it from past IBM systems.
Although HDDs existed since the 1950s, the cost and expenses were far too great to make it an addition to regular systems. Rather generally, the systems came in with a Floppy-disk reader, used to read 5 ¼” disks, branded “A” in many OS including DOS. Some systems came in with two readers, initiating the need for “B”. As it was rather generously used, “A” and “B” for floppy drives remain entrenched even today.

Towards the end of 80s, when HDDs became standard, as the first two letters were already used, the letter “C” came to be associated with hard-drives.

Even today, though floppy drives are now practically non-existent, the lettering schema is still followed, of course if you have administrator rights on your system, you can still change them to your liking.


I started this tech blog back in 2011 as a place to write down processes I took to fix my client systems and network. Now I write some tips and tricks to help others with the tech issues that one might encounter.

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