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This is a question that just popped into my mind and I can't help but wonder why it's still common for a Windows installation to be installed on C: with all other drive letters going up from D: to Z:. In the early MS-DOS times, all we had were floppy disks and they were at A:. When the 3.5 inch floppy started to replace the 5.25 floppy, many people had an A: and B: drive. Then the hard disk became popular and the hard disk was at C: because A: and B: were taken. Then the 5.25 floppy disappeared and most computers had a gap between A: and C:. Nowadays, the 3.5 floppy is just too outdated so A: disappeared too. All disks now start at C:.

Yeah, I know I can assign my own drive letters and I've done so with my data disks. My installation disk will just continue to be stuck at C: and I don't really mind. I have no problems with drive letters.

But why do the new Windows versions just continue to install themselves by default on C: instead of assigning the letter A: to the boot hard disk?

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Of course I wonder why windows continues to use drive letters at all. Why not just mount everything into a single tree? – Zoredache Jul 1 '09 at 21:22
Too proud to adopt anything from Linux maybe? ;-) – David Z Jul 1 '09 at 21:43
Some of us like the multiple root directories that drive letters give you... – Moo Jul 1 '09 at 23:13
@Moo: chroot ;-) – Dennis Williamson Jul 2 '09 at 0:57
My computer ended up with its primary hard disk labelled J:, no C: at all, and it's not easy to change it back. Almost everything still worked, but most installers would get confused and require you to supply a path manually. – pjc50 Nov 20 '09 at 13:53
up vote 11 down vote accepted

I believe that it probably has more to do with legacy then it does moving forward. Despite the fact that A and B were taken and C became the default hard drive assignment, most applications assume that C is the default OS location, A and B are floppies, and D is CDROM or DVD drives.

I've seen applications break if the default OS is not located on C.

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There are also those out there who still run a floppy drive, and would get very confused if it wasn't at A as "it wasn't first in the list" – RascalKing Jul 1 '09 at 20:51
If we were moving forward, we'd abandon drive letters altogether :) – Kevin Kuphal Jul 1 '09 at 21:31
Because all of our computers would exists in the cloud... :-p – RascalKing Jul 1 '09 at 21:32
Mounting everything on one tree makes sense too. Of course it would confuse the people who are used to drive letters. – David Z Jul 1 '09 at 21:45
+1 for noting that one of the main reasons is crappy 3rd party applications. – Niels Basjes Sep 28 '09 at 14:26

Some (badly written) software, including parts of Windows assumes that the OS drive will be C, and will crash/fail if this is not the case. Microsoft doesn't want to break stuff, so they've left the default as C.

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A lot of Microsoft software assume C: exists and is writable. Try installing Office to D:. It'll work, but it will still put a lot of files onto C:. – staticsan Jul 1 '09 at 23:07
I do like that more recent Microsoft software depends on the environment variables and Registry entries for finding the Program Files path. That said, I still have recently used a practice of mounting extra drive space (Apps drive) to an empty NTFS folder under C:, rather than make it a D: or E: drive. – mpbloch Apr 13 '10 at 23:32

When I built my last home machine using Vista, I tried to use A: & B: for the CD-ROM drives. I forget all of the problems with that I encountered, but Vista was clearly not amused.

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+1 for "vista" and "amused" in the same sentence. Sense of humor required with that OS! – Kara Marfia Jul 2 '09 at 13:59

Just because there is no reason to change. Changing from C to A can only break things and doens't do anything working better.
Most application wouldn't have problem to run even if C: is not the system drive but you may have custom scripts running on your server with hard path to some file (exemple if you have a software to analyze apache log file) and if you reinstall your server you probably don't want to have to check every config files or script to change path.
You just want to copy them from old installation to new one then run and it works.

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I've used other drive letters like D: for my Windows partition (and then A-C for data partitions) since Windows 2000 without a single problem so this is just tradition. If there's some software that won't handle it, I haven't seen it...

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Why change? What advantage would it give? Something like this needs a reason for change and so far nobody has come up with anything that would warrant such change.

As for dropping the use of drive letters altogether, the same argument applies. There are pros and cons both ways, with neither being a clear winner.

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I'm okay with the primary disk being C:, but I'd like my flash drives to be seen (by default) as A: & B:. At least they would have purpose again!


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Although if you plug a USB floppy in, it's seen as A: – Tubs Jul 2 '09 at 11:03

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