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Windows 7: Changing Drive Letter of Boot/Active partition

22 Dec 2012   #11

Window 7 Home Premium 64-bit

The screenshot was taken on 21 Dec. 2012 just prior to the reinstallation of Win7CL on the left-most partition, and shows how Win7CL sees its own system partition with drive letter F when booted into Win7CL. After the reinstallation, which was recommended by you (gregrocker), and performed on 21 Dec. 2012, Win7CL now sees its own system partition with drive letter C. Infact, both installs (Win7CL on the left-most partition, and Win7OEM (drive Z)) associate the drive letter C to their own system partition; whatever OS I boot, its own system partition shows the drive letter C. So all is OK now.

I've always been in the tacit assumption that the Win OS Installer, in my case the Clean Installer, makes sure the newly installed Win OS, when then later booted into, sees its own system partition/volume with drive letter C, no matter the Win OS installer was running from an external USB drive, another Windows version on the HDD, or from DVD. I've always been under the impression that the association of drive letters to any partition/volume is contextual, meaning just local inside the registry of each Win OS on the system HDD. All the different Win OSs on the system HDD shouldn'd care how any another OS does the drive letter association. That was the picture I had in my mind until recent, and I think this must be the same what you explained in your post, if I interpret you post correctly.

So, in whatever boot cofiguration the Win OS (Clean) Installer runs, the newly installed Win OS (when booted into) should always see itself with drive letter C, but ... that was not the case on my computer; Why is that? I don't know.

With me it raises another question about drive letter association to system partitions/volumes: when does the drive letter association really take place during/after a Win OS installation? Is that:
1) done by the Win OS Installer which associates the drive letter C to the newly installed system partition in the registry key HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices of the newly installed Win OS, or is that
2) done by the newly installed Win OS itself when it boots for the very first time?

In case 1) is the answer, then I wonder why the Win OS Installer doesn't give a clear WARNING when the Win OS Installer is about to associate a drive letter to the system partition/volume different from C? Folks who are not very familiar with installing a Win OS, will probably not notice that the Win OS Installer wants to associate a drive letter different from C to the system drive; they don't pay any attention to the drive-selection screen, just as I did. Hence that I think the Win OS Installer should give a clear warning when it wants to write a non-C value into the registry key HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices for the system partition/volume drive letter of the newly installed Win OS.

In case 2) is the answer on previous question, then ... ... what? ...

Regards, j

My System SpecsSystem Spec
22 Dec 2012   #12
Microsoft MVP


Again, for about the 4th or 5th time now:

The Win7 installer only correctly installs to C when it is booted, not run from another OS which is C.

If it's run from another OS on C, that letter will be locked out and unavailable to use without reinstall from the booted installer.

This is not a mystery and has been the case without fail since we started here before Win7 was even released.
My System SpecsSystem Spec
23 Dec 2012   #13

Window 7 Home Premium 64-bit

Gregrocker, now I got test confirmation about what you've been telling me all the time.

Today, 23 Dec. 2012 (@10 am), I've done the Clean Installation *again* but from within the booted Win7OEM version (which sits in partition Z in the screenshot). The Win7OEM saw its own system partition as C, and the left-most partition as F, so all was ok. I've then put in the 4GB USB Flash Drive (UFD) with the Win7 Clean Installation and started the setup.exe file, which sits in the UFD root directory. The Clean Installation went well and the new Win7 Clean Installation (Win7CI) was put in partition F (in the screenshot). After I booted into Win7CI, Win7CI saw its own system partition as F and the Win7OEM partition as drive C, so it was back to the old situation prior to 21 Dec. 2012. This confirms what you've been telling me.

Today, 23 Dec. 2012 (@5 pm), I did the whole Clean Installation all over *again* but this time after having booted form the Clean Installation (CI) UFD, so no booting from the internal system drive. I assume the running OS must be some kind of WinPE version. Result, when booting into Win7CI, Win7CI sees its own system partition with drive letter C, and the Win7OEM partition has the drive letter D, so all is ok again.

The "missing link" in this whole discussion is the following explanation: When booting from the CI UFD, a RAM disk is probably created which WinPE uses as system drive, and probably that RAM disk has drive letter X, so very different from C. I noticed there must be a RAM disk because the CI UFD also contains a "repair disk" and in that repair disk I went into the Command Prompt under the System Recovery Options. That Command Prompt window showed me X:\Sources> and that was the moment when I realized the Clean Installer sees its own (RAM) disk with drive letter X.

It is only now, after several reinstalls, trials, tests and of the discovery of the RAM disk's drive letter X, that my fuzzy mind fully comprehends (I hope) what you've been telling me all the time: by design the local system drive letter in the newly installed Win7 cannot be the same local system drive letter of the Win7 Installer's boot partition/drive. That is how it is by design (I think). Gregrocker, thanks for all the time you've put in clearing up my mind.

Still got second thoughts, though, about why the Win7(-Installer) designers took that decision about drive letter association. As the drive letter association is very much contextual, that is, done locally within the registry of the booted OS, any booted OS could in principle associate any drive letter to any visible partition (including its own system partition/volume) with the only and single condition that all visible partitions must have a different drive letter. Actually, I think it would've been a whole lot easier if the designers simple dropped any drive letter association in Win7.

Regards, j
My System SpecsSystem Spec


 Changing Drive Letter of Boot/Active partition

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