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My friend is trying to install Diablo 3 in his windows 7. But he kind of messed up a little with his partitions.

All his files (and also extra space) are in the drive A, but his OS (windows 7) is running from drive C

Every time he tries to install Diablo, he change to drive A but it says "invalid directory" and doesn't save anything there, but instead, it suggest the drive C (where there is no space left).

Could it be because A is originally for Floppy disk? How could he fix it?

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up vote 3 down vote accepted

My guess is that the installer is based off of some ancient technology developed in Blizzard's dark ages and, as you suspected, you cannot install on either a drive lettered A or B. As noted, this is because these were the floppy or other external media drives from a long time ago, and it simply won't recognize them as a valid install location.

You must change the drive letter to something NOT A-C (D is always a wonderful choice) in order to install Diablo III and commence the looting.

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Thanks, I'll hit him (again) for creating in the directory A – Michel May 15 '12 at 14:16
@Michel it could be worse - once I flubbed a Windows install and ended up with the OS on drive I:\ and the data drive as J:\. Real good way to flush out poorly-coded installer programs! – Steven May 15 '12 at 21:20

Try subst:

Simply go to a command prompt and type

subst d: a:/diablo3

Then install to D:.

Once it's installed, move it wherever you actually want it.

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Assuming his drives are both formatted NTFS, you can try using the mklink command described here:

I would do that with whatever folder he will be installing into, and then run the installer.

Although a different situation, I use this trick to move games that I already have installed on my HDD onto an SSD without re-installing them.

Effectively, you can make a folder on 1 drive look like it's actually a folder on another drive. This is done at a very low level in the NTFS filesystem API, so the end-user software doesn't even seem to know. I was worried this could agitate sensitive applications (i.e. PunkBuster), but it doesn't.

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Have you tried right clicking on the Diablo III setup file and choosing 'run as administrator'? I had the same issue and 'run as admin..' solved it and it installed just fine.

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