Some years ago (actually decades now), when Windows 95 (or even 3.11) came, "A:\" and "B:\" partition names were reserved to the old magnetic removable discs (also known as Floppy Disks).

However, today it is a forgotten standard and we don't see it embedded anymore on any new machines(actually, if you need to buy a floppy disc today you will spend more money that it was if buying a Flash card, at least in my country it is not easy to find it selling anywhere)machines.

So I was wondering if these are still reserved on new version of Windows Systems (Vista, 7 or even on 8) and if I could use these partition letters to install another Operating System, use as a backup partition, work partition (with data and application files) or even to install my main Windows 7 system?

It is still recommended to install Windows on "C:\"? I mean, should I use "C:\" for Windows to avoid application incompatibilities or something like this? Is there any additional information related to A:\ and B:\ that would prevent me to install Windows over these partition names?

  • 2
    Of note: when I inserted a USB floppy disk drive into my Windows 7 laptop, the system assigned it A:. As such, current versions of Windows still use these drive letters for FDDs.
    – bwDraco
    Sep 1, 2011 at 19:17
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    Just for the record, this convention predates all Windows versions, going all the way back to CP/M and later MS-DOS (AKA PC-DOS) as well.
    – yosh m
    Sep 1, 2011 at 21:43
  • 1
    Also directly related - What are the Windows A: and B: drives used for? Sep 3, 2011 at 0:13
  • I assigned B: to an external drive that I use for backups. Quite convenient: B stands for backup. Feb 15, 2013 at 7:57

5 Answers 5


Drive letters, such as A: B: C: are not partitions. Partitions are logical divisions on storage media. Drive letters are logical assignments to a file system made by the OS. Drive letters can be removeable media, hard disks, and other parts of a file system. Windows will reserve the A: and B: drive for floppy disks, however you can assign other volumes to A: and B: if you desire in disk management.

  • 2
    You didn’t answer the question. Can you install Windows in A: or not? (That’s a legitimate question because starting in the middle of the alphabet for historical reasons seems silly if it is avoidable. It seems logical to start at the very beginning; it’s a very good place to start.)
    – Synetech
    Dec 16, 2013 at 5:32

I would stick with C: for compatibility reasons, as you suggested. I'm sure that lots of programs out there just assume that the primary drive on Windows machines is C:, just like some programs assume that all Windows machines have the same path for My Documents or other common folders. I've definitely had problems with programs opening "Save as..." dialogs in nonexistent folders and either generating error popups or creating unwanted directories.

Sure, it's the programmer's fault, but you're going to be the one stuck with software that doesn't work, so....

That said, I agree with the contents of Keltari's answer.

  • 4
    Sure, it's the programmer's fault, but you're going to be the one stuck with software that doesn't work, so. I was looking for someone to say "it's the programmers fault!". Glad someone pointed out that it is irrelevant when your software is either out of support or the developer just doesn't care and you still need it. Sep 20, 2011 at 20:07
  • I used to have Windows installed to drive D: as drive C: was taken by Windows 9x. I don't remember I encountered applications that stopped working because of D: (however, those app still found a copy of Windows on drive C:). Yet I saw many apps that believed Windows always speaks English and created "My Documents" on localized version of Windows. This stopped to be an issue since Vista which always uses English folder names on the file system. Feb 15, 2013 at 8:02
  • Compatibility is the correct answer. Even if it can be done (Windows won’t let you), it should be avoided in most cases because many programs (including Windows itself) still use old libraries that assume A: and B: are reserved for floppies, and many programs, especially old ones are actually hard-coded.
    – Synetech
    Dec 16, 2013 at 5:33

As other pointed out partitions and drive letters are not the same thing.

In Windows 7 if you go to [Control Panel] > [Administrative Tools] > [Computer Management] > [Storage] > [Disk Management] you will see all your partitions (even optical drives, floppy drives, and flash drives).

If you right click on a partition/device there is an option [Change Drive letter].

You could make your "Windows" drive A:, your CD ROM P: and your USB drive: Z:.

Now before you go crazy. There is no good reason to do so. Programmers SHOULD reference the boot partition by variable thus if you change it then the program will still work but programmers are often lazy. They may hardcode their application to look in C:\WINDOWS\SYSTEM32 for example. They shouldn't but some of them do. If windows isn't on C the application is going to die.

Partition =/= drive letter. Drive letters are merely labels. Something that helps us humans relate to computers. Windows sees it as a series of devices and partitions. Nothing more.


AFAIK since Windows Vista the system partition always gets "C:" independent of the drive letter you installed it onto.

  • Which is a good thing; it really simplifies double-booting.
    – Synetech
    Nov 8, 2011 at 18:12
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    I also thought so until I accidentally installed it to drive D:. Windows drive will always be C: if you install Vista+ by booting from install DVD, even if you select not the first partition for installation. On the other hand, if you start Windows setup program from a running copy of Windows, then the new copy will keep the assignments of drive letters. That's how I installed Vista to drive D:. Feb 15, 2013 at 7:54
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    @AlexeyIvanov, thanks for the clarification. I installed Windows 7 from the DVD and it used C: even though I already had XP installed in C:. I was both amused and pleased to find that Windows was installed in C: when I booted XP and when I booted 7. Thanks to your warning, I know to avoid running the setup program from within Windows (which for the record I would never do anyway, but still, good to know).
    – Synetech
    Dec 16, 2013 at 5:37

I have just installed Windows 10 in drive A: . I believe I can do it using Windows 7 also as the installation system is similar.

This PC showing Windows installed in drive A:

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