CD and DVD images

If you have ever lost a valuable CD or DVD because of a scratch or general wear and tear, you’ll know the importance of creating a backup copy. Depending on the type of content you are backing up, there is a way to both back up your discs and gain quicker access to your disc collection without having to juggle CDs or DVDs in and out of your drive. The technique is known as imaging, but more frequently it is called ‘creating an ISO’.

An image is an exact copy of data stored on media — floppy images have been around for years, and hard drive images play an important role in backing up entire operating systems. Few people know it, but CDs and DVDs can also be imaged.

What’s the point?

Before heading off and creating ISOs, there is a question that needs to be answered — why make an image of a CD or DVD when all you need to do is copy or even zip the contents of the disc? The short response is that, in many cases, you don’t need to create an image at all. A CD full of photographs will hardly benefit from being turned into an image. However, there are a few instances when creating an image will save time and minimise the chances of files being lost or corrupted. The most common is backing up software installation or game discs.

If you have ever delved into the contents of an installation CD, you may have found it was chock full of files scattered across a hundred buried directories. In most cases, if you start moving the files or leaving out folders because you think they serve no purpose, there is a good chance the installation will stop working. These kind of unintentional alterations can’t be made on a CD-R, but it is surprisingly simple to do if you copy thousands of files to your hard drive (or zip them without maintaining the directory structure).

An ISO ‘locks’ the content, meaning you can’t easily change the files within it. Unless you have a specialised ISO editing program, the way to change an ISO is to burn the image to CD (or load it to a virtual drive — more on that later), copy the files back to a hard drive to make changes, and finally create a new ISO. This is hardly a process that will happen by accident.

Once you have an ISO, it can be backed up or sent to other users (very popular with Linux distributions). Depending on their sizes, you can back up multiple ISOs onto a single CD or DVD.

There is also the issue of file management. An ISO is a single file. If you have copied 20 CDs onto your drive and each contains over 1000 files, this adds over 20,000 files to your hard drive. With the increased load of files, your searches, system-wide antivirus scans and defragmentation will all be slower compared to having just 20 ISO files.

Virtual drives

A virtual drive acts like a CD drive, except that files are loaded from your hard drive. Specifically, they load an ISO image and let you access the contents just as if you had inserted a CD. This speeds up access to the files because hard drives are much faster than CD drives, and you don’t have to swap discs and wait for the CD to spin up/spin down. Click here to see a screen shot.

There is a chance you already have a virtual drive program: Nero includes a frequently overlooked virtual drive called Nero ImageDrive. A free alternative is IsoBuster (see the cover CD for a free copy). This utility works a little differently — it loads the image, but doesn’t assign a drive letter.

What type of CDs or DVDs can’t you image?

It may seem obvious, but the whole idea of copy protection for CDs and DVDs is to stop people copying them. If the CD or DVD has copy protection, it is unlikely that the ISO will function correctly. When the ISO is opened, the program usually will ask for the original CD to be inserted into the drive or will give an obscure error message.

Unfortunately, it is not always obvious that a disc has copy protection. The two most frequently protected file types are commercial DVD movies and game discs. Both systems can be defeated and many Internet sites are dedicated to these topics. The most famous is DeCSS, the tiny program that breaks the encryption techniques designed to stop duplication of DVDs (for more information, search Google for ‘DeCSS’). Next month we’ll look at ways to create ISOs and convert between the various formats. In the meantime, have a look at the free versions of IsoBuster and Burn4Free on the cover CD.


As noted in the introduction, many people refer to CD and DVD images as ‘ISOs’. In a wider context, anything associated with an ISO normally means it conforms to a well-defined standard that everyone follows. Unfortunately for CDs and DVDs, this term has been bastardised, with the result that not all ISOs are the same. ‘ISO’ images come in wide varieties such as ISO, BIN/CUE, NRG and CIF. This can create headaches because of compatibility issues between different programs. For example, Nero 6 can burn NRG, ISO or BIN/CUE files, but Easy CD Creator 6 is limited to CIF and ISO. Even having the ‘ISO’ extension won’t clearly tell you the type of file structure the image contains.

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Scott Mendham

PC World
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