What is Disk Imaging?Disk Imaging is the term used to describe the process of creating image files of physical disks, both harddrives and CDs/DVDs. Do not confuse the term 'image files' with picture files that contain images, like .JPGs, BMPs, .PNG and .GIF, etc.
These disk image files are exact representations of the contents of the disks that have been imaged. They are NOT the same as just copying the files on the disk to a folder or a single file. Image files contain
extra information that cannot just be copied using Windows Explorer or a similar program. That extra data includes things like physical disk errors and boot partition information, amongst other things.
How is it useful?These image files can be used instead of using the actual physical CD/DVD/HDD. Because they exactly replicate the physical disk, they can be used in situations where software verification requires that an original disk be used. The use of these image files saves you from having to find your original CD/DVD every time you want to run a particular program or play a particular game. Using the image file also saves your optical drive and original disk(s) from wear-and-tear. Another benefit is that access to the image file on your harddrive is
much faster than access to the physical CD/DVD in your optical drive.
How can you create images files?You can create an image (or 'clone') of your CD/DVD using software like Alcohol 120%, BlindWrite, Nero Burning ROM, UltraISO, CloneCD/CloneDVD and others.
These software packages will allow you to specify which disk you'd like to image, and some even allow you to create an image from files and folders in different locations. Alcohol 120% allows you to specify a range of other options, like whether it should include physical disk error infomation in the image (some software looks for this information to verify that the original disk is being used).
In the past, I've used Alcohol 120% to create images of my original Blizzard CDs, because other cloning/imaging software created images that failed to pass Blizzard's verification routines. Recently, though, I've had a host of problems after installing Alcohol 120%. Your mileage may vary.
Note that there are a lot of different extensions for these image files, like .CUE, .BIN, .ISO, .BWT, .CDI, .B5T, .CDD, .MDS, .NRG, .PDI, etc. The ISO extension is by far the most popular, so much so that image files are often refered to as ISOs.
How do you use such image files?Once you have an image file in one of the abovementioned formats, you need to mount (or load) the image into a 'virtual drive'. Software like Daemon Tools, ISOBuster, VirtualCD, Alcohol 120% and CloneCD/CloneDVD allows you to create a software drive on your computer that appears to be a physical drive to your operating system. You can 'insert' this disk image into this 'virtual drive' using methods that are specific to each piece of software. Using Daemon Tools (recommended), you would right-click on the Daemon Tools system tray icon, navigate to the virtual drive sub menu, and select the Mount option. Select your image file, and click on OK.
In essence, this will load the image file into the virtual drive, exactly emulating inserting a CD or DVD into an optical drive (complete with Autorun functionality).
As mentioned earlier, you can also make an image file of a physical harddrive. Why would you want to do that? Well, in the case of Norton Ghost (in the past) and Acronis TrueImage (currently), you can store an image of your current installation of Windows, in case something happens to it (harddrive crash, virus, registry corruption, etc, etc). Windows XP System Restore does this, but on a limited scale, because it only stores details about the registry and a limited set of files. Using TrueImage, you can create a backup image of your entire harddrive, including boot information. If anthing goes wrong with Windows, you can use the image to restore it in just a few minutes.
The only negative to using image files is that they consume a large amount of disk space. An image of a full CD will occupy 700 megabytes of your harddrive, and an image of a full DVD will occupy 4.7 gigabytes. An image of a physical harddrive may consume many gigabytes, depending on how much data is on the drive that was imaged. But with the size of harddrives increasing and the price of harddrives decreasing, this is not really a major drawback any more.
I hope that I've managed to clarify some of the issues surrounding disk imaging. If not, there are loads of resources on the web that
probably describe things much more clearly ;)
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