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Can you have 2 C: partitions on one disk?

I was having a discussion/debate yesterday with a friend about dual-booting machines. We can't agree on whether or not two partitions on a single disk can both be called "C:" when booted into. He said you can modify the registry for each instance of Windows so that the system volume is "C:", but I've never been able to make this work.

I said you absolutely cannot have them on the same drive letter, although I couldn't  explain why to his satisfaction.

The question is - is there any way at all that you can have a dual booting machine using the C: letter for each instance of Windows? Even if that means hiding the other partition, or unassigning the drive letter.

Please help us settle the debate - if the way to do it is relatively complex, please post instructions as we'll want to test it out.

Avatar of purplepomegranite
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It may be that you technically can, though I have not tried this.  I would also think that this would not be a desired option (at least, I can't see that I would want this).
There is an article here:
It describes how to change the system drive letter in WinXP.  If any method is going to work, I guess that will.  I don't know of a method for Vista, so ensure that Vista is installed to the C: drive, and XP to the other -then try changing the XP drive letter as per the article.
The answer is absolutely YES!

There is no drive letter until the operating system is loaded

So the drive is simply called ROOT or SOTRAGE DEVICE.

Since each partition has it's own Operating System, then each Operating system will have its own Drive C.

More explanation:

ROOT starts up with boot.ini
Gives you two Windows Options.
Each Window will assign it's own drive letters to it's own partition
Since the OS doesn't care about the other OS then Windows will assign the C letter
>>Since the OS doesn't care about the other OS then Windows will assign the C letter
No it won't if the machine has been dual-booted using any of the recommended methods.  The installation of the second OS is aware of the first during install, so assigns letters appropriately - so if you have a partition for each OS, by default one will be on c, one on d (for example).
I agree with the rest of your statements though - letters are assigned by the OS, there is no reason why each OS can't assign a different letter to the same drive.
On all my dual partitions AFTER windows loads, they are both C
If that helps any.
And yes, you are correct... the Windows setup cares about the other Windows, but once Windows is on, after boot.ini they are holding the C letter
Fair enough.  Out of interest, how do you set up the dual-boot?
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Back about a year and a half ago, I had a computer on which I multi-booted Windows 98se, Windows ME, and Windows XP.  I used Partition Magic to create the multibooting system; when I booted into each version of Windows, each of them thought they were installed on drive C: and after I "unhid" the other partitions, they of course were other drive letters.  But this came about only because I used the standard way of installing another operating system using Partition Magic, which "hid" previously installed OS partitions during the install process.

Now, Partition Magic doesn't work in Vista, but I had it working with XP.  I am not sure whether other partition managers can hide already installed OSes so that the new OS you're installing thinks it's on C: drive.  If you use the standard way of installing a second OS that uses the system drive's OS loader, then the second OS will be installed on a drive letter higher than C:.   See this tutorial, for example, on how to dual boot with XP with Vista installed first:

and this one for dual booting XP with Vista with XP installed first:

With traditional boot managers, it very much depends on just how the OS install was done -- it assigns the drive letter at installation time and it is not easily modifiable.   As you can tell from the above discussion, different folks have seen different results even with the same boot managers => the difference is indeed in just how they did the installs ... NOT with the specific boot manager.

As LeeTutor noted, if you use the "standard" way to install a 2nd OS using the Windows boot manager, the OS's will have different drive letters for their system drives (C:, D:, etc.).

You CAN, however, have as many OS's as you want installed --- ALL using the C: drive -- by managing your multiple boots with Boot-It NG, which is a superb boot manager; partition management utlity; image and restore utility [ ].   It uses a special extended MBR (EMBR) structure that overcomes the 4 primary partitiion limit, and lets you set the MBR that any specific system "sees" -- so they ALL think they're installed to the first partition ... and thus assign C: as the drive letter.    On the system I'm typing, this on, I can boot to XP Home, XP Pro, XP MCE, Vista Ultimate, XP x64, Vista Ultimate x64, UBuntu, and KBuntu => and they ALL have a "C:" drive.   Here's the boot menu from a few months ago (I haven't updated this ... so it doesn't show XP x64):

... by the way, I have another (older) system I use for booting to just about anything I might want => it has 15 different OS's on it ... ALL on the same disk; and ALL boot to C:
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The debate rages. What I can take from this is that there isn't a native way of getting 2+ OS's to cohabit, with each booting to C: but there are many tools to fix it. At least I haven't seen a compelling description of how it's possible to achieve without employing a third-party tool. The link to Petri's site is pretty much identical to a MS article I read today and it didn't work - it wouldn't get past the install Windows XP Professional screen which appears just before you are asked to login on a worksgroup PC. I tried this several times just to be sure.

I'll close this question on Monday evening after I've been into our office to test it out. We use Altiris, and I've got a single XP image which I'll drop onto a test PC for each app suggested. Using each suggested app I'll recreate the image on a second partition if possible, or I'll run a quick XP install.

I'll award the points based on the simplest and cheapest/free tool as if they all work I'll need some criteria to judge them by. However, if someone can post a complete description of how to set it up without using a third-party tool they will get the points, as this was the centre-point of our original debate. Assume I've tried modifiying the keys in "HKLM\SYSTEM\MountedDevices"
Typo in first para. Should read:

it wouldn't get past the Windows XP Professional logo screen which appears just before you are asked to login on a workgroup PC

[This is when the screen goes blue, after the Win XP progress bar you get subsequent to POST]
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Gary Case
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Sorry for the late response. I've been working with some different partition managers for the last few days, and BootIT wins hands down. It is powerful, simple to use and unobtrusive once installed (and free, depending on your scruples). I bought a copy of this and Image for Windows yesterday - really impressed that it will take full backups of Vista and Server 2003 from the same software and all for £26.50/$49.99. It did take a few goes to get right, but I had backups to work with, so no dramas.

I think BootIT wins just because I don't know what I've been doing without it, it's so versatile and powerful, and all from a very simple interface - also, it could probably do with the promotion over Partition Magic!
Good program, thanks for the tip. I'll be an advocate of it from here on in, and I've tried Symantec, Acronis and MS tools as well as others. This is excellent. All booting to C: now !
Agree ... I've used virtually all of the major players => and Boot-It is far-and-away the most reliable; best-focused; and amazingly versatile.   And at a VERY reasonable price.   I wouldn't dream of building a system without it !!