Changing the drive letter of System Drive

[John Gray]

I have moved my dual-boot Windows 7 Pro 32-bit and XP Pro laptop from a 200GB drive to a 750GB drive using Macrium Reflect's Clone feature, and on the way reordered the partitions and increased their sizes. This was fairly successful.

However, the drive letter allocations (as seen in Disk Management) have changed since the days of the 200 GB drive.

What I want is:
when booting to Windows 7
Win7 C: (boot, system)
Data D:
WinXP E:
and I get this OK

when booting to Windows XP I get:
Win XP C: (boot)
Win 7 D: (system)
Data E:

but what I want (and had previously on the 200GB drive) is:
WinXP C: (boot, system)
Data D:
Win7 E:

I don't actually mind if, in XP, Win7 E: shows as System, but I want the Data drive to stay as D:, regardless of which operating system I boot. I can't change the Win7 E: in XP, because Windows won't allow me to change the System or Boot drive letter.

I'm quite happy to mess with DiskPart and BCDedit and the Registry Editor, provided someone can say what to do!

Any thoughts, please?

[jonwallace]

These two knowledge base articles describe how to do what you want, I think.
http://support.microsoft.com/kb/307844" onclick="window.open(this.href);return false;
http://support.microsoft.com/kb/223188/en-us" onclick="window.open(this.href);return false;

BUT they contain dire warnings that changing a system drive letter will make the system unbootable.

[John Gray]

Thanks, Jon, but I was trying to change the drive letter within Disk Management, which gave me the "Can't change System or Boot drive letter" message...)
Unless I misread your second reference, they appear to be assuming that their drive D: is both System and Boot, and this wants to be changed to C:. I have separate System and Boot drives (at the moment)... I will examine it further. (I already had to change XP's BOOT.INI (from within Windows 7) to cause it to boot from drive 3 rather than drive 1, because otherwise XP would not boot.)

[John Gray]

Well, here's what I find in the MountedDevices key...

MountedDevices.PNG

As you can see the value data for \DosDevices\C:, D: and E: is each matched by one of the {items-in-curly-brackets} higher up - but that's as far as I can go...

[John Gray]

And it seems that the value data entries are composed of an four-byte disk signature followed by an eight-byte partition offset. (See Editing the MountedDevices Registry Key, which doesn't do anything for my Boot or System problem.

[jonwallace]

And it seems that the value data entries are composed of an four-byte disk signature followed by an eight-byte partition offset. (See Editing the MountedDevices Registry Key, which doesn't do anything for my Boot or System problem.

It all makes perfect sense to me.....

[John Gray]

Well, I've plucked up courage and interchanged the D: and E: value-names, and rebooted.... and it's worked!
I now have:
WinXP C: (boot)
Data D:
Win7 E: (system)
which is good enough for me. Thanks, John, for the pointer!

[jonwallace]

I knew you could do it!