IMG vs DMG - best practices archiving CDs

I think this was discussed in the previous incarnation of 68kmla but I can't find it anymore.

I am going through all my media to archive it for eventual posting to vintageapple.org, and other places. Floppies are easy with Applesauce.

I'm a little confused about the best way to archive CDs. I started by using Disk Copy 6.3.3 on OS 9 on a Lombard. Kinda slow. It is producing IMG files. In one case, where a CD has both a data and audio component, they both showed up as mounted disks and I had to create images of both.

I assume the eventual goal here is to allow mounting directly from within the OS, as a disk image, that can be used like the CD would. I know this will work for macOS 9, but will it also work on System 8 and System 7?

What about archiving via a modern mac and Disk Utility? Is a DMG or .cdr (which is just an ISO right?) usable?

Any guidance here would be appreciated. I've got quite a lot of CDs to archive, so I want to get it right before I get too far in.

Well heck, with some of the CD's, I can't create an image via Disk Copy on Catalina. They must be HFS format or something, not a standard CD format.

I believe best archiving practice for hybrid CDs is still to produce a BIN/CUE combination, because that maintains information about the track layout, whereas ISO/DMG/IMG only maintain information about the data portion of the disc. However, these usually require third-party tools to mount, and so you are likely to have to make a decision between ease of mounting and accurate archiving in these cases, because an ISO or a pair of raw images won't properly preserve the structure of the audio part of the CD.

For data-only CDs, ISO or cdr is the best option: I generate them with dd, and I'm happy to tell you how I do that if you would like. ISO files are just raw images of the data part of the disc, so should be able to contain any filesystem that can be on a CD.

Yes, I'd be curious how to do this with DD. Do you think it will work on a CD Catalina Disk Copy won't make an image of?

I'm going to post this tomorrow morning, if you don't mind: I'm too addled right now and I want to find you actual concrete examples.

Oh, and can OS 9, System 8, System 7 mount ISO images easily?

pcamen said:

Oh, and can OS 9, System 8, System 7 mount ISO images easily?

Click to expand...

Yes. Sort of. For best results, I always used Toast CD Rom, and the right version for the right OS. Toast 2.5.8 for System 7, Toast 3.x for OS 8, and Toast 4.x for OS 9. You load up Toast, select your ISO, and click 'Mount'. It mounts it on the desktop for you. Easy and simple.

For saving out ISO files that are on CDs meant for Mac System 7 and before, I use Astarte CD-Copy 2.0.

To add, Windows ISO utilities like infrarecorder make good ISO images of most Apple CDs, I've had good luck using infrarecorder and imgburn to make and burn images of Classic Mac OS boot media. (I have some at http://vtools.68kmla.org/~/coryw/iso-temp/ for example)

ISO does not work very well on actual Classic Mac OS systems. There are some utilities that can mount them (Toast and some other smaller more shareware/freeware oriented tools), so preferences and process here will ultimately come down to how you want to use things. I tend to leave my 7/8/9 machines as bare as possible so for anything I'm going to use once I have an OS installed, I use Disk Copy 6 images, unless the image/media/disc is complicated enough to merit using a bin/cue.

So, my strategy is:
ISOs for media that'll get used to boot Macs
DC6 images for media that I want to mount on a Mac over the network to install application software or fetch data
DMG images only for application software and/or data transfer that only runs on Mac OS X. (DMG should work for OS X boot disks but it would be better to use .CDR or .ISO to make it easier to burn the discs on non-Mac computers.)

I suppose we all have our routine. For CDs, I only have to worry about Mac discs myself (having no Windows machines), so every CD/DVD I have all become .CDR format first because of being able to make an easy (and as Cory mentioned if necessary) bootable copy of said media. I only normally burn discs on OS X-based machines, so this is no issue for me at all. As for being able to mount, I use Virtual CD/DVD-ROM utility to mount the .CDR images without issue on my machines. ReadMe states it works all the way back to System 7 with appropriate CD extensions installed. The other day, I mounted my Marathon Trilogy .CDR I made from my own discs on a G4 under OS 9 with no issue.

As for floppies, I make all my floppies into .img DiskCopy 4.2 format. I do not care for myself if there are block-for-block copies, or if the magnetic flux of a certain sector was off by so much and all that...I just want the software backed up and to work when I need it. DC 6 format is fine...unless you try to use the image on a Mac that can't run DC 6. That is why I go with 4.2...it works on them all.

Turns out I can't give you concrete examples today because something extremely unfortunate seems to have happened to the USB port on the back of my external CD drive (i.e., has been ripped totally off the board. Sigh.)

The trick is to use


to list the partitions on the disc, then carefully pick the one that you're going to use. This isn't the ISO partition scheme, it's usually the first one under it. This might be a bare HFS filesystem, it might be an Apple Partition Scheme, it might be an ISO9660 FS.

This is the bit that Disk Utility often gets wrong, by the way; it sometimes decides to image just the filesystem as well as the partition map and the filesystem, which means that the driver and the partition scheme and other stuff that makes the disc bootable gets lost.

Then use something along the lines of


replacing X and Y with the numbers from the device that diskutil told you about.