Drive letter allocation

johne53 · 29 May 2010

Does anyone here happen to know how Windows decides which partition (and on which disk drive) should be allocated as C: ?

The reason I'm asking is that I recently bought a new Mac Mini and immediately installed Windows 7 onto it using Apple's Boot Camp utility. This meant that I could dual boot between OS-X or Windows 7. Since buying the Mac I've been looking for a safe way to backup and restore partitions (a job that I used to do previously using Paragon's 'Drive Backup' app).

Unfortunately, Drive Backup isn't (yet) compatible with the GPT partitioning scheme used by Apple. This meant me having to look further afield and a product called Active Disk Image was recommended to me. The first time I tried to make a clone my Windows partition I was horrified to see all the icons disappear from my desktop and I immediately cancelled the operation. From then on, Windows 7 has been unbootable. Whenever I try to boot it I see a message saying "autochk program not found - skipping AUTOCHECK" and then Windows shuts down.

autochk.exe is definitely present (I can see it if I mount the Windows 7 volume under OS-X) so I strongly suspect that Active Disk Image has somehow nobbled my C: drive so that it's no longer being allocated the letter C. My suspicion was strengthened when I saw an entry in a log file suggesting that C: had been renamed to ?: The makers of Active Disk Image are investigating this but they don't seem to have much sense of urgency.

Fortunately, my old stalwart (Paragon's Drive Backup) comes with a sector editor and Paragon's apps are normally pretty reliable. So if I could re-allocate my C: drive by editing an appropriate sector entry, I could hopefully be back up and running again.

Or isn't it that simple?

Jonathan_King · 29 May 2010

Windows will boot from whatever the active partition is, or where the boot loader instructs it to boot from. It then assigns whatever partition it boots from the C letter.

I suggest a startup repair from the Windows DVD or repair disc.

A system restore to get to a point before the troubles may also be in order.

johne53 · 29 May 2010

Thanks for the quick response. It's definitely attempting to boot (I see the Windows logo and the green progress bar beneath it) but then it gets to a stage where (apparently) it can't find a program which is definitely in the right place.

At this stage I'm slightly loathe to attempt a System Repair in case I end up unable to boot OS-X (I know from bitter experience in the past that Windows repair utilities often have a habit of assuming that Windows is the only important OS on the disk - and royally nobbling any other OS!) Nevertheless I'll keep that in mind if I can't find any other solution.

[Edit...] I tried your second suggestion and luckily managed to fix the problem by using System Restore to rewind to an earlier good configuration. Thanks for the tip!