When you mention TORRENT, you are talking of a file extension, which works on a basis of networking system.
The onus lies in the distributor-recipient relationship.
In this file extension, the recipient enhances the networking system, and that is the sole reason, why this extension works in an inexpensive manner.
How does this happen? The process involves hosting and bandwidth costs.
The distribution network created out of this extension helps in spreading the hosting and bandwidth costs evenly, and that results in cheap working of this format.
Apart from distribution of data, there is a peer-to-peer sharing process.
One such example of peer-to-peer sharing could be seen at bit torrent.
Both features make it a very attractive extension.
The file extension DMG is entirely a different prospect.
It is compatible with Mackintosh operating system, designed by Apple.
It can be difficult to understand how this extension works.
It is a significant file for mackintosh OS.
The operating system from Apple looks at DMG files as a real disk.
DMG files are created out of disk, perhaps by burning a CD.
DMG extension is not compatible with Windows, but you may face a problem running such files, if you have both Mackintosh and Windows in your system.
Initially, you will get baffled, and find difficult to understand why your system has not been unable to run them, in spite of your system having mackintosh OS.
It's important that you have the current version of the operating system installed in your computer, to make DMG extension work in your system.
PC with Windows operating system converts DMG file to image disk one, but it's important for your system to have DMG to IMG application to convert DMG to other files.