I thought that using the same hard drives with different Windows operating systems should not be something problematic but I had several occasions when a hard drive that was used with a previous system was turned into unallocated space from a newer Windows OS.
For example I have an external USB hard drive that used to be used with XP for several years and after I tried to use it on a my new Vista computer, Vista automatically installed a device driver for the hard drive requiring restart after which the the drive was listed as unallocated space in the Disk Management.
Also recently I decided to upgrade to Windows 7 and installed it on the same computer that used to run only with Vista. Right after installation Windows 7 had no problem using all my hard drives. But once I booted from Vista and back from Windows 7 again, it installed automatically device drivers for all data hard drives requiring restart after which all my data hard drives were listed in the Disk Management as Unallocated space.
What's happening? How does Windows decide a device driver is needed for my data drives when initially there were no problems. Where is the information containing the device driver? On the system hard drive or on each hard drive? Do different Windows OS use different device drivers for the same hard drives? Why installing a device driver for hard drives has to turn disk drive into unallocated space and thus the data inaccessible from the system?
W7 does the boot management process differently, but I can think of nothing that would cause this. Do the drive come back once repartitioned and then are usable going forward with both bootabel OS's? Is there some other boot management or partition management software running?
In the first case with the external USB there was no other boot software involved.
In the second case yes, I'm using BootIt NG. Its a boot program that installs on the hard drive and loads before Windows Boot Manager. It prevents Windows from seeing different OS installations on different hard drives and forces it to use only one installation instead of messing with different OS versions and confusing the boot process. Before that I tried to use the Windows Boot Manager after installing Windows 7 on a separate hard drive. But there were serious problems. Even though in the BIOS of the mobo I disabled booting from all other hard drives except the one I want Windows to boot from, Windows Boot Manager always examines all available hard drives for system files on them and if it finds any it will start messing with them thus destroying both the inactive systems and the active one. I think, Windows 7 Boot Manager can boot properly in Windows muli OS environment only if it was installed when the other system was visible to it, so it becomes aware that there is a previous system already installed. And then also, the computer must always run with the two systems being available all the time. If for some reason one of the system is not available (for example unplugged hard drive) and then available again, on the next start up systems self destruction begins. This is very poor boot managing. Now using the third party program BootIt NG solves this problem but the problem remains with the the device driver installation making all data hard drives unallocated space. And this is not a problem with BootIt NG. I can reproduce this every time by following these steps.
1. Install Vista and Windows 7 independently from each other on separate hard drives (no other system should be present during installation, that is, boot system hard drives should be unplugged)
2. Run the computer only with one of the systems and additional data hard drives.
3. After switching to Vista and then back to Windows 7, device drivers for the additional data hard drives will be automatically installed turning the healthy data and the rest of the hard drives into unallocated disk space that can be used only after reformatting and loosing the data.