PDA

View Full Version : iso v dmg - whats the difference



lenman74
11th March 2009, 12:49 PM
Hi

I want to create backups of my optical discs including media and installer discs.

in disc utiity I can create disc images but they are .dmg files.

Three questions that I have are:


1. Will these DMG's be ok to burn exact replica's of the original discs?

2. will the DMG's once, mounted, be recognised as if they were the same disc.

3. Do I need to bother with creating ISO's vs the DMG's?

Cheers
Len

LCGuy
11th March 2009, 12:51 PM
You're best off sticking with ISOs...just about any CD/DVD burning program will handle an ISO with no trouble, on any platform, whereas generally only Mac software will handle .dmg's.

lenman74
11th March 2009, 12:55 PM
does disc utility create iso's? or toast?


edit: disc utility can create .cdr's and toast can create .toast files

i have read that both of these are iso files but maybe with a little extra.

if I wanted maximum compatibility which would you go for

.dmg, .cdr or .toast ?

tekrox
11th March 2009, 02:02 PM
does disc utility create iso's? or toast?


edit: disc utility can create .cdr's and toast can create .toast files

i have read that both of these are iso files but maybe with a little extra.

if I wanted maximum compatibility which would you go for

.dmg, .cdr or .toast ?

a .cdr is just a .iso with a different file extension - rename it .iso and BOOM! one iso created!

lenman74
11th March 2009, 02:13 PM
cdr it is then, cheers

i have also found a utility called isolator which also creates iso images

csuter
11th March 2009, 03:54 PM
I want to create backups of my optical discs including media and installer discs.

in disc utiity I can create disc images but they are .dmg files.

Three questions that I have are:

1. Will these DMG's be ok to burn exact replica's of the original discs?

2. will the DMG's once, mounted, be recognised as if they were the same disc.

3. Do I need to bother with creating ISO's vs the DMG's?

I'll tell you what I know. The details might not be exactly right but they're pretty close to the truth.

A DMG file can take a number of different formats. They are defined by Apple. There are, amongst other formats, compressed types and sparse types as well as the plain old read/write format.

An ISO file, I believe, is an uncompressed direct image of a CD/DVD. Usually they contain ISO 9660 file systems (commonly used on CDs) and possibly UDF file systems (commonly used on DVDs). I'm not sure if it's legal for them to contain other formats—probably not. Your OS X installation media doesn't use either of these formats.

If your DMG happens to be in the read/write format, the DMG file is uncompressed and looks exactly like your CD/DVD (there's no header). You can rename the file and give it an IMG extension and use it in other programs (such as on Windows). Otherwise, OS X will need to be involved in order to access them.

OS X will allow you to mount ISO and DMG files. They effectively look just like regular disks.

You can burn ISO and DMG files to CDs or DVDs using Disk Utility and you'll get a CD/DVD that's identical (unless you're dealing with a CD/DVD that has copy protection measures).

You can convert from DMG to ISO without too much trouble. If you want to archive these images, use a compressed DMG format.