Apple's wonderful Disk Copy utility gives you the ability to create
a disk image - a file which pretends to be a mounted disk - which the
operating system treats as a real disk. This is a short tutorial that
explains how.
You'll find the Disk Copy utility in the Utilities Folder, which is
inside the Applications (Mac OS 9) folder on your OS 9
computer. There is also an OS X version included with newer
machines that does exactly the same thing.
The process is actually very simple. If the CD-ROM consists of
simple files and folders, with no encryption or hidden files, simply
insert the CD-ROM in your drive and wait for it to mount. Then start up
Disk Copy and choose Create Image from Disk under the Image menu.
Disk Copy creates a disk image file that contains the actual data.
This file appears on your desktop - or wherever you specify to save it
- as a file ending with ".img". It then proceeds to attach to this file
information which is exactly the same as found in the hidden directory
structure of any mounted drive on a Mac. This includes the desktop
information file, for example, that users cannot normally see or
directly access.
After zeroing out the new "disk," the OS is told to mount the file
as if it is an external drive, such as another CD-ROM or a FireWire
drive or whatever. It then appears on your desktop as a blank disk.
When you choose the "Create New Image" command, and the disk is ready
to receive data, just drag the contents of the CD-ROM onto the mounted
image, and, in many cases, you're done.
Since no one has an infinitely large hard drive, you should do a
"Get Info" on the source disk to see how much data there is to copy.
When Disk Copy asks you to set the size of the image file, your image
file should be at least this large.
On simple CD-ROMs, this works great. You can remove the CD-ROM and
return it to your protected archive (read: Kmart CD pouch). Then, when
the disk is needed on the computer, you just double-click on the .img
file and the copy "mounts." No CD - no problem.
You would think that many manufacturers would take steps to prevent
such easy duplication, and you'd be right. Many software disks, at
least for the Mac, contain a few hidden files that the Mac OS doesn't
display and cannot be manipulated with a mouse. These files do not show
up in a directory listing, and the don't add in to the total file size
in a Get Info. Thus, when you use a "Create Disk Image," they aren't
copied because you didn't allow enough room for them. When attempting
to use the mounted image, some file that is crucial to the program (but
invisible to you) will inevitably be missing.
The solution is pretty easy. Instead of using the "Create Disk
Image" command, use the "Create Image From Disk" command. This will
copy the invisible files as well. You still need to estimate the image
file size, and if you are trying to save hard drive space that may take
some trial and error. But if you have an 80 GB hard drive, it will hold
many CD-ROMs without any difficulty, so you could specify a size
slightly larger than a CD-ROM's capacity and get every file
possible.
On older Macs, you might have to play around with the size a bit for
maximum efficiency. Machines with drives smaller than 1 GB will
probably have difficulty preparing more than 1 or 2 CD-ROMs as disk
images. You also get a compression option when saving the image, so
this would be a good time to use it.
If you place the image or an alias of it in your Startup Items
folder (inside the System Folder), it will automatically mount with
verification when you boot your machine. If you want to get rid of the
verification step - which is really unnecessary since you have the
original CD-ROM anyway - then you can write a short AppleScript to
mount the images without verification, a command that is understood by
Disk Copy when in a script.
I have used this technique on as many as 20 CD-ROMs (all of which I
own) simultaneously, and all the the disks mounted just fine on the
desktop.
Of course, you shouldn't exchange the image files unless both
parties involved own the software. Also, this technique doesn't work on
audio disks; for that you have iTunes.
is a longtime Mac user. He was using digital sensors on Apple II computers in the 1980's and has networked computers in his classroom since before the internet existed. In 2006 he was selected at the California Computer Using Educator's teacher of the year. His students have used NASA space probes and regularly participate in piloting new materials for NASA. He is the author of two books and numerous articles and scientific papers. He currently teaches astronomy and physics in California, where he lives with his twin sons, Jony and Ben.< And there's still a Mac G3 in his classroom which finds occasional use.
