sepdek November 28, 2012

Some years ago I got my macbook air and in a flash of genius I got a 200GB USB disk to use as a backup disk (time machine backup disk). This was great and there where a couple of times it prooved really useful.
Recently I wanted to detach this USB disk from its primary usage as a backup disk and use it regularly as a Windows disk. As expected, due to the different file system used on Macs, when I connected it to my Windows PC there was no Drive letter assignment. Nevertheless I was able to recover whatever files I needed using HFSExplorer, which I have been using for a long time now. Only this time I wanted to change the disk itself. I wanted to convert it to the NTFS file system since I would be using it as a typical USB disk.

The thing is that Windows does not provide a mechanism for doing this conversion within the “Computer Management” GUI, which can be accessed by right clicking on “My computer” and selecting “Manage”. What Windows provides is a means of doing it through the command window (“cmd” nowadays).

Once I opened a command window using the Start/Run/cmd command (in administration mode) I executed the DISKPART program, which activates a subsequent shell of options regarding low/high level disk operations. Here I run a couple of commands to see what’s going on and figured it out.
First I had to check which Disk is the Disk I wanted to convert and to select it. This can be done by using a few commands:

list disk

The first command shows the disks available to the system at this instance. I got the following response:

DISKPART> list disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online           57 GB      0 B
  Disk 1    Online          298 GB      0 B
  Disk 2    Online          465 GB  1024 KB
  Disk 3    Online          232 GB  1024 KB
  Disk 4    No Media           0 B      0 B
  Disk 5    No Media           0 B      0 B
  Disk 6    No Media           0 B      0 B
  Disk 7    No Media           0 B      0 B
* Disk 8    Online          186 GB      0 B        *
  Disk 9    Online          465 GB  1024 KB

Results showed that Disk 8 (the one with the “*”) is a GPT disk and is the disk I wanted to convert.
The second command was a command to select the Disk (disk 8):

select disk 8

I got the confirmation:

Disk 8 is now the selected disk.

And finally, the magic was done by using just one simple command:


which resulted in:

DiskPart succeeded in cleaning the disk.

After the Disk was clean I could manage it easily. I used

convert mbr

to convert it to MBR (although I suppose it was not necessary), with the response:

DiskPart successfully converted the selected disk to MBR format.

After that I closed DISKPART and the command window, since I was able to use the typical GUI-based “Computer Management” of windows to do things on this disk as normal.



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