.DMG files on a PC

Hello! The .dmg file is the Mac image file format. PC's aren't gonna read it much like the Mac is not gonna read a .exe file. Tom

Abe

Disk images are formatted with the "HFS +" file system. This cannot change, definitely not with disk utility and I am not even remotely aware of a third party utility that can do that.

Use Toast or similar and burn in either ISO9660 (preferred) or Joliet.

Windows boxes will then be able to read the CD.

I believe OS X itself only formats HFS+

Windows, however, will not be able to open the DMG file.

Hi, Abe.

Is it that the PC could not read the CD or the disk image?

CDs burned in Finder are compatible with Macs or PCs running Windows. See "Mac OS X 10.4: Creating a CD Formatted for MS-DOS (Windows)."

However, while "Disk Utility 10.5 Help: Formatting a disk for Windows computers" states:

"When you create a disk image you can erase it and change its volume format so that other computers, such as MS-DOS for Windows computers or UNIX file system computers, can read it."

Under Tiger, I've not found a way using Disk Utility to create or change a disk image with a Mac volume format to one formatted with the MS-DOS file system. Hence, a disk image created on a Mac using Disk Utility won't be readable on a PC unless the PC is running an application like Mediafour's MacDrive for Windows.

With Tiger, disk images now always use the Mac OS Extended file system. Under Panther, one could create disk images using the MS-DOS and UNIX UFS file systems, but that's been removed from Disk Utility under Tiger.

One can use the hdiutil command in Terminal to create a new, blank, Read/Write disk image, or an image from a folder, that uses the MS-DOS file system by including the

-fs MS-DOS

flag in the command.

For example, the following Terminal command:

hdiutil create -srcfolder ~/Desktop/Test -fs MS-DOS -volname DOSTest ~/Desktop/DOSTest.dmg

created a disk image:

• from the folder Test on my desktop ( -srcfolder ~/Desktop/Test)

• in MS-DOS format ( -fs MS-DOS)

• with volume name of DOSTest ( -volname DOSTest) so that when it is mounted it shows as volume "DOSTest" in Finder.

• with the disk image saved as DOSTest.dmg on my desktop (the last parameter, ~/Desktop/DOSTest.dmg).

The command produced some error messages, i.e. two instances of

mount_msdos: /dev/disk3: Resource busy
/sbin/mount failed with error 18176

during the creation process which I have yet to explore, but it turns out the resulting disk image appears fine and mounts on my Mac. It mounts as volume "DOSTEST" (vs. volume name "DOSTest" but -volname may be case insensitive).

Disk Utility shows the mounted volume as having:

Format: MS-DOS File System (FAT-16).

One could then try burning that disk image to CD and seeing how a PC handles it. I don't have a PC running Windows handy at the moment, otherwise I'd try that. 😉

Hope that helps.

Good luck!

😉 Dr. Smoke
Author: Troubleshooting Mac® OS X

You want to specify the original folder in -srcfolder.

When you create a disk image — remember, it's a virtual hard drive saved as a file — the file system is embedded in the disk image. The disk images you created with Disk Utility have, by default, "Mac OS Extended (Journaled)" as the file system.

Defaulting to "Mac OS Extended (Journaled), IMO, is a bug I've reported to Apple. By defaulting to Journaled, one sees journal-related errors in Console when you mount a Read Only disk image created in Disk Utility since the Journal can't be updated! They should use "Mac OS Extended", i.e. non-journaled, for Read Only disk images. They should also expose more of hdituil in Disk Utility. It was "dumbed down" in Tiger...

Good luck!

😉 Dr. Smoke
Author: Troubleshooting Mac® OS X

Hi, Abe.

This is a really good opportunity to start learning a little Terminal. I think you're up to the challenge! What's keeping you from trying it?

Why do you want to create a disk image to use to transfer the files to the PC? Why not simply burn the files to one or more discs if you have to physically move the files from the PC to the Mac? If the PC and the Mac are on the same local network, why not use file sharing to copy them from the Mac to the PC?

Maybe you should clarify what you're trying to accomplish and we can suggest alternatives.

Good luck!

😉 Dr. Smoke
Author: Troubleshooting Mac® OS X

I think what we are missing is your ultimate goal -

My guess is for whatever reason, you have a group of files that are currently stored as a DMG. You want to be able to open those files on a windows box

But the windows box can only be used to store a DMG.
No matter what you do with it, Windows will not be able to open the DMG.

so..

If your goal is to get the contents of the DMG file on your mac to the windows box, then the easiest way to do that is:

1. Mount the DMG on your Mac (2x click it)
2. open the mounted file (icon should look like an external floppy drive)
3. Copy the contents of the now mounted DMG file to a Toast window
4. Burn an iso formatted disk.

The PC will then be able to work with the files on the disk.

I agree with AJ,

But, rather than messing with Toast, you can just burn the files directly to CD or DVD from the main Finder (desktop) window.

Just drag the files from the disk image into a folder on the desktop.

Then, insert a blank CD or DVD, and let it mount on the desktop.

Then, drag the the folder (or just the files from the folder if you like) into the mounted CD-R or DVD-R disk. Then, burn the disk.

You can either right-click on it and select burn, or dragging it to the trash can should present you with a burn option.

Also, you can skip the step of copying them from the disk image to your desktop / folder if you like. In this case, just copy them straight to the CD mounted on your desktop.

If you already have Toast, and prefer working with it, then by all means use it if you like. But, you should know that you do not need to use Toast just to burn data CD's and DVD's that can be read on both PC's and Mac's.