After installing OS, When opening "MY Computer" it shows first hard disk as "C", why so?

Why Hard disk labeling starts with C rather than A?

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    My immediate first thought was: "What a stupid question! Obviously, A: and B: are the floppy drives! How could anyone not know that?" … My second thought: "Man, I'm old!" Nov 8, 2015 at 4:39
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    I am 24 years young and I know the answer. Does this mean I am too old! :O
    – sohaiby
    Nov 8, 2015 at 6:37
  • @sohaiby indeed, in 1990s floppies were still actively used, so even those who are 20 would still know this.
    – Ruslan
    Nov 8, 2015 at 6:39
  • I miss you floppy ;( Nov 8, 2015 at 11:28

2 Answers 2


Because History.

As you can see any self-respecting IBM PC from the early 1980s had two 5-1/4" floppy drives (black):

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The first floppy drive, the one on the left, is A: and second, the one on the right is B:. When one of those new-fangled hard-disks was added, it became C:. All software assumed that this was how the drives were labeled.

Eventually, when the hard drive became standard, any application program that needed to access an operating system file, it knew to look for it on drive C:. Over time, floppy drives slowly disappeared. But, the assumption that key OS files were on drive C: remained. That is why the first hard disk is C:.

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    Also because basically every machine had a floppy controller with support for two drives and there wasn't much of a way to establish the absence or presence of the drives themselves. So A and B were effectively permanently reserved.
    – hobbs
    Nov 8, 2015 at 5:23
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    Windows itself is capable of living at any path (in fact it doesn't even need drive letters at all, they're just symbolic links to UNC paths!) but other software might be less flexible, and so might users. :)
    – hobbs
    Nov 8, 2015 at 5:25

C:\ is the default drive because Windows is built on DOS. In early DOS computers there wasn't a hard disk; only floppy drives. These were A:\ for the first one and B:\ for the second if the computer had two. By the time hard disks came around, A:\ and B:\ were taken so C:\ was used for the default hard disk. We still use C:\ because to maintain compatibility with older software.

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