Thursday, December 6, 2012

Why do Mac applications that are downloaded from the internet come in .dmg files, but not an .app file?

Q. Whenever I download an application from the internet and not the Mac App Store, the app comes in a .dmg file, why not just an app if you don't have to install those apps that come in .dmgs?

A. a .dmg is a disk image. It is very similar to a .iso, except it has encryption and compression options.

a .app is not a file. It is a folder... the call it an Application Bundle. If you use terminal, you can cd through it like any other folder. In Finder if you want to see inside of a .app you have to right click and choose Show Package Contents. Its just a normal folder, but Finder knows if the folder ends with .app to hide the insides... and knows how to handle trying to "open" that special folder.

You can create a folder in Finder and name it something .app and play around with it.. it will act like a broken application in Finder since the internal folders and files won't be right to be a real app.

Being that a .app is really just a folder, you cannot download folders, they need to be a single file. That can be a zip, or rar, or dmg, or whatever... Apple just prefers making it a disk image over a Zip.

If I have the an application installed on my Mac, do I still need the DMG of the app?
Q. The reason I ask is because I'm cleaning up my computer and I want to know if I can delete the DMG if the app is installed and then after deletion have the app still work.

A. I like to keep them to save downloading them again should I need to reinstall (especially large downloads) but rather than leaving them on the hard drive taking up unnecessary space, burn them to CD/DVD and store that way.

Install Mountain Lion.app to Install Mountain Lion.dmg?
Q. Hi, I have recently joined the apple developer program and downloaded the Mountain Lion Developer Preview, but i don't want it to be the operating system that my computer runs, i want to run it as a virtual machine in Parallels Desktop 7. I am currently running Lion 10.7.3. I have already tried to make a virtual machine for it but it tells me that no operating system is installed, so i need a way to convert my Mountain Lion.app to a DMG file.

A. "I have recently joined the apple developer program"

Perhaps you should spend a bit more time on the Apple Developer Program. You can burn Mountain Lion as a .dmg in Disk Utility. It will not make any difference. Mountain Lion is a preview version and will not be supported in Parallels or other virtual machines. You can install it on a separate drive and boot into that to test your software with it.




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