Why is the Main Drive in Windows Called C:?

If you use Windows (the operating system, not the glass viewing device) and have ever worked with files at all, you know the main drive in Windows is called C:. Typically there are other drives as well, such as D: for your disk drive and E: for a flash drive or other such device. The next drive you add will then be F:, then G:, and so on, going further into the alphabet. But something is a bit strange about this setup. Why does this pattern start at C? I know Pluto got canned (a moment of silence), but last time I checked A and B were still letters.

Drive Letters

The use of letters to denote drives seems familiar to us now, but like many other operating system conventions it originated at some point. Several decades ago (a bit after the dinosaurs), there were actually many operating systems, and the market was much more fragmented. One of these was called CP/M. CP/M made use of drive letters for physical storage devices. Around the time CP/M roamed the earth, Microsoft and IBM got together and made MS-DOS, the text-based precursor to Windows. In an effort to compete with CP/M, MS-DOS was made to be compatible with many of CP/M’s conventions, including drive letters, so that existing CP/M software could be easily ported over to MS-DOS. This strategy was successful, which is why nobody knows what CP/M is anymore. Naturally, Windows borrowed conventions from MS-DOS, and so the drive letters are still in use.

This history lesson was fun, but it doesn’t actually answer the question: what happened to A and B?

Floppy Disks

Ah, the good ole’ floppy. Old enough, as it happens, that I have never actually used one. They are likely more familiar to you if you also have fond memories of the sound of a dial-up connection. Nothing is quite as nostalgic as yelling at people using the phone line. Whether or not you have used floppy disks, you do know what they look like – they have become the standard save icon in software, that blue thing. This icon has been retained despite floppy disks becoming obsolete shortly after 2000.

Floppy disks used to be quite widespread. If you used a computer, you used a floppy disk – they contained your operating system, as well as your programs and data. Typically, you would insert a floppy disk and boot from it. Then, you would take out the boot disk, and insert another floppy disc before using the program stored on it. If you were a lowly peasant, your computer only had one floppy drive, so these disk swaps occurred quite often. The king, on the other hand, had the luxury of two floppy drives. That is double the floppy, folks.

At the time, hard drives weren’t really a thing. It later was the hard drive, among another things, that replaced floppy disks. The boot drive, where the operating system was located, was a floppy disk. This disk, then, was the first physical drive, and therefore was given the letter A. B, then, was given to the second floppy drive, if you had one. Floppy disks were so ubiquitous that by de facto (bam, fancy words) convention, A was the first floppy drive, and B the second. This remained the case for over a decade. By the time hard drives were on the horizon, existing software assumed (typical software, always making assumptions) the primary drive was the floppy disk, A. If hard drives, the new main disk, were given the letter A, existing software would break. And people just don’t like broken software very much.

So, for the sake of backwards compatibility, the first hard drive is given the letter C. This practice has been retained in every version of Windows, and presumably will be in use for quite some time. A and B, on the other hand, are no longer in use, unless you happen to still be using floppy disks. In modern Windows, you can actually use A: and B: for existing drives if you modify some settings, though this would be done mostly for stylistic reasons as there are plenty of other letters. Some software is written badly, however, and much like with floppy disks, assumes the Windows drive is always C:, which isn’t necessarily the case. Due to this, it is probably safest to stick with the defaults.


Jacob Clarity


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