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I have just reinstalled Windows XP on my machine and something weird happened.

I have a DATA partition which used to be I:/ but now after reinstalling it's name is C:/ and the system partition's letter is I:/.

The PC is booting on I:/, I can reboot and the new system boots without any problems.

But it's impossible to change letters back, when I try to change C:/ (DATA) to O:/ it tells me that I am unable to change the letter of the partition containing the system!

I haven't tried to change the I:/ (system drive) because I'm afraid I won't be able to boot at all any more.

Partition layout

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Are these partitions all on the same drive or separate drives? –  Mokubai Dec 21 '11 at 19:11
    
Yes, it's on the same drive. I really don't know how this happenned. Maybe when I was partitionning the drive again (deleted the ancient system partition and I recreated it). Maybe the other one switched to C:/ at this moment, but so why isn't it D:/ for the new one ? –  PatrickCUDO Dec 21 '11 at 19:17
    
Could you post a screenshot of your window in disk management? It might help just to see what is going on. The only times I've seen this happen is when there was already an existing Windows install on the drive but if you say the you deleted the partition then that is a bit odd... –  Mokubai Dec 21 '11 at 19:20
    
img833.imageshack.us/img833/79/diskk.jpg Here you go. On this pic I tried to change the letter of the DATA partition. I'm french, so I have put a translation of the error message. But basically, the whole problem is exposed in this frame. –  PatrickCUDO Dec 21 '11 at 19:27
    
What do you mean by reinstalling? Did you format the disk or an inplace upgrade? –  kinokijuf Dec 21 '11 at 19:49

2 Answers 2

up vote 4 down vote accepted

By the looks of the screenshot you posted it would appear that you have accidentally created your first partition as an "extended" partition (with your boot "Demarrer"? as a logical partition within it) rather than as a "primary" partition. You can tell an extended partition from a primary partition as an extended partition has a green border and contains other partitions.

As a result it appears that Windows has made your first partition the boot partition (where the bootloader is stored) and put all the system files on the first primary partition it could find.

Typically having an extended partition before a primary partition is highly uncommon and it may be that this is a bug in the Windows Installer. I think I might be right in that you can only boot from primary partitions and so it could be that the Installer set the first primary partition ("Data") it found to be active and bootable, then installed system files to it and then set up the bootloader on the partiton you told it to install to. As it had already set up the system files on the data partition it then continued to put the rest there. A very ugly state indeed.

The easiest way to rectify this problem would be to reinstall your copy of Windows after deleting the 20GB partition and recreating is as a fully fledged primary partition using something like a GParted LiveCD.

There'd a short read on Primary and extended partitons on Wikipedia

-=EDIT=-

Based on kreemoweets comment I have checked and he is indeed correct. The "boot" partition stores your system files and the "system" partition stores the files needed to boot in the first place. (Which makes no sense to me at all)

This reinforces my belief that the extended partition is the problem.

An extended partition cannot be set as bootable, only a primary partition can. As such Windows installed the bootloader on the first usable primary partition (your data partition) and because in Windows Primary partitions are enumerated for drive letters first, it gets first call on the C:\ drive letter in Windows.

As you told Windows to install the system files on the extended partition it is likely that it has done this properly, but because it is not the booting partition and additionally is not a primary partition, it gets allocated a drive letter after other devices.

My earlier recommendation still stands, recreate the first partition as a primary partition, and reinstalling should almost certainly fix your problem.

You may end up with NTLDR and some other files left on your data partition after reinstalling, but so long as that partition is no longer the "System" (or boot :S) partition, the they should be safe to delete.

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Ok, so I'll have to reinstall it one more time. I didn't know that windows works this way, regarding partitions. I really appreciate your help, thank you very much. –  PatrickCUDO Dec 21 '11 at 20:50
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Recall that, in Windows parlance, the "boot" partition is the one containing the OS files, whereas the "system" partition contains the boot files. There seems to be ongoing disputes between Windows Disk Management and other partitioning apps as to, for instance, what an extended partition actually is. I would seek a second opinion from something like GPartEd. –  kreemoweet Dec 21 '11 at 21:00
    
I'll be back physically to this machine in a couple days. I will post the information I'll get from GParted, just for curiosity's sake. –  PatrickCUDO Dec 21 '11 at 22:02
    
Here's the gen on system and boot volumes, again. –  JdeBP Dec 23 '11 at 14:54
    
Ohh, nice, thanks @JdeBP –  Mokubai Dec 23 '11 at 15:56

you can boot a linux liveCD and install grub as the boot manager only. it has options to mask partition order on the booted system. depends how much work is reinstalling for you.

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