What the hell is a .dmg all about then?

Discussion in 'macOS' started by dogbone, Oct 3, 2005.

  1. dogbone macrumors 68020

    dogbone

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    Sep 16, 2005
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    #1
    I could have a folder of stuff.

    But I don't have to. I could make the folder of stuff into a .dmg file then when I click on it the .dmg file mounts on my desktop. In the mounted folder is my "stuff".

    Why?

    OK I am able to encrypt the .dmg but is this the only reason for the existence of .dmg or does it have other qualities.

    What does it mean exactly that a .dmg file will "mount" on the destop. What is the difference or relationship between the .dmg file and the image that 'mounts' on the deskop that looks like a HD icon.
     
  2. khammack macrumors regular

    Joined:
    Sep 28, 2004
    Location:
    Portland, OR
    #2
    DMG is short for Disk iMaGe. It is just that, a file that acts like a disk. It's uses are many:

    * As you mentioned, .dmgs provide a convenient way to encrypt a bunch of files. You can drag the .dmg onto an external drive or ipod to tote it around, if you so choose.

    * If you haven't already noticed, you will find that most Mac software is provided on compressed .dmg files. It is a very convient way to package and distribute software over the web; just download the dmg, mount it and drag the app to your applications folder.

    Mounting a disk image makes it accessible as a normal disk (rather than just another file whose contents you cannot see). This is just like "mapping" a drive to a drive letter in windows. Conversely, to "unmount" a disk image means to disconnect from it so that you can no longer access it's contents.

    In unix systems, disk drives are not assigned letters. Instead, additional disks are "mounted" so that then entire contents of the disk looks like just another folder on your hard drive. OSX is not exactly a UNIX system, but it is very closely related and has much in common with a standard unix system.

    -kev
     
  3. ravenvii macrumors 604

    ravenvii

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    Melenkurion Skyweir
    #3
    DMG files are used mostly for transportation. You can't download or email or whatever a folder. But you can with .dmg files. Because, well, they're files. :) And being mountable, you can set your preferences (background color/image, icon size and position, window size and location and form and stuff) and when someone else opens and mounts a DMG file, there it is, all your hard work in beautifying it.

    For stuff that you don't intend to send to others in groups, use folders. You can encrypt folders too (FileVault).
     
  4. dogbone thread starter macrumors 68020

    dogbone

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    #4
    If I want to send one biggish file, say about a 20 Mb pdf over gmail for example, is it better (better meaning more reliable) to make it into a .dmg file and send that or a zip? or is it a mac only thing.
     
  5. 840quadra Moderator

    840quadra

    Staff Member

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    #5
    Mostly a Mac thing. Sending a .zip is more universally accepted.

    [​IMG]
     
  6. sebisworld macrumors 6502

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    Jun 24, 2003
    #6
    Is there even software to open DMGs on a Windows box?
     
  7. DeSnousa macrumors 68000

    DeSnousa

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    Jan 20, 2005
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    Brisbane, Australia
    #7
    Change the .dmg extension into a .iso extension. Then grab a free .iso extractor for Windows. Do a '.iso' search on version tracker to grab an app.
     
  8. iEdd macrumors 68000

    iEdd

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    Aug 8, 2005
    Location:
    Australia
    #8
    I think you can considerable cut down on a file's size when sending it, by putting it in a .DMG, then making it a sit or sitx file :)
     
  9. mkrishnan Moderator emeritus

    mkrishnan

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    Grand Rapids, MI, USA
    #9
    FWIW, they're also good for creating virtual disks in a different file system than the host disk -- invaluable for emulators, for instance, in which it is nice to have an NTFS, for instance, disk available on your system, but you don't want to re-partition to get it. :)
     
  10. Flying Llama macrumors 6502a

    Flying Llama

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    Aug 4, 2004
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    Los Angeles
    #10
    I for some reason really like DMGs, I wish everthing on the net were compressed with 'em. Especially ResExcellence which has a knack for stuffit...

    llama :eek:
     
  11. EGT macrumors 68000

    EGT

    Joined:
    Sep 4, 2003
    #11
    Disk images are handy. One thing though, when you have run out of space on a particular image, can you enlarge it without having to make a new one and transfer data across?

    Sparse images only take up the amount of file size of it's contents. Is there anyway for the .dmg to expand automatically as stuff is added?
     
  12. mkrishnan Moderator emeritus

    mkrishnan

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    Jan 9, 2004
    Location:
    Grand Rapids, MI, USA
    #12
    You can make sparse .dmg's in OS X, but you cannot make them compressed and sparse at the same time, sadly. :( It's an option when you create the disk image; it should be pretty straight-forward.
     

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