1 Reply Latest reply: Sep 29, 2010 9:12 AM by a brody
Jaden Pretzlaw Level 1 Level 1 (0 points)
Hello all,

I was just wondering if anyone could explain to me the process that a .dmg file undergoes once it's downloaded from a website? I seem to have noticed that when you initially get the file, a installer document comes with it (dmg.part) and when you try to mount the disk image it says that it isn't recognized.

After struggling with it for quite some time it eventually works...and furthermore smaller programs like MSN messenger I never had problems mounting th image. What's causing the time laps with allowing me to mount the image? Do I have to wait for the installer document to do something? In time the installer document disappears and then the disk image increases in size from 0 KB to maybe a couple 100 MB. Is there something I'm missing here? =/

Any help would be appreciated, thanks in advance!


MBP, Mac OS X (10.6.4)
  • a brody Level 9 Level 9 (64,380 points)
    DMG files are encapsulated disc images. They act like real discs once you double click them, by providing a volume that mounts on your desktop to drag the file out of, or double click an installer. If the DMG file is not downloaded completely, it should not be opened. Your Download manager for your specific browser should tell you when the download is complete. If your default folder for downloads is your desktop, you'll see two files often by the same name, one with a different icon than the other. Once the download is complete, you'll be able to double click one to reveal a folder or installer for the installed file. Some of them are compressed as .gz or .zip, and some as .hqx or .sit files. Until all such suffixes are removed from the file name, they are not mountable. The operating system has built-in .gz and .zip support. .sit and .hqx support was dropped I believe with 10.5, and you need to download Stuffit Expander from http://www.stuffit.com/ to expand them.