How To Access And Work With Virtual CD/DVD Image Files

This article is slightly more advanced than some of my previous articles, and will explain to you incrementally (a concept at a time) how to create and use image files. I will then discuss three different methods that you can use to read them back, and how to make Windows and other operating systems use those files as if they were physical CD or DVD drives. Finally, this article makes its conclusion with detail for the reader to better understand how and why disc formats behave as they do on certain hardware and facts that may help to overcome those things.

If you enjoy a good read and like my other articles (but wanted more technical detail), then this is a good start for understanding the basics of image files, and how they tie together with cross-platform systems and emulated machines.

OK, let's begin:

Whenever you copy a CD, normally the data is copied off of the CD onto what is called an image file.

The image file is a perfectly identical snapshot of a CD, disk, or other media.

Most CD images are called ISO files (ISO is the standard universal format for CD images), but they may at times come to you as a combination of two other files called Bin and Cue files. Bin is the shorthand label for a binary file (a file which contains all the data you want to burn to a CD for example), and the Cue file is like a cue-sheet, which tells a CD burning program where, when, and how to start burning the data to a disc. While those files are still used sometimes, they are rare to encounter. If you do encounter them, you can always convert those files into 1 ISO file. You won't have to worry about them most of the time (unless you get into some serious bootloader CDs and non-standard formats).

CD images may come as .cdi or .nrg files as well (nrg is generally used by a popular program called Nero). But again, there are free tools online to convert between these formats for you on several different platforms, and 98% of the time all the CD images these days come stored and are distributed to others as the standard ISO file format.

When you are ready to create an image of a CD or DVD, you can create one using a commercial software solution such as PowerISO...or a freeware program that is fast and efficient called LCISO which I prefer personally.

Commercial programs like PowerISO often have a lot of useful features, but if all you need to do is create an image file, then LC ISO is what I would recommend. It runs on most versions of Windows immediately after setup, it uses little ram, it is fast, it is easy, and it is free. It will create an image out of just about any CD or DVD disc that you give it. Because this program merely reads the disc data byte by byte and creates an image file out of it, you will not ever need to worry about it whether you are affecting the original physical composition of the disc or not. It is read-only. Only the digital image file (the mirror image of everything that you've read off of the disc) is created/written to a file. Nothing else.

To obtain LC ISO free of charge and begin making disc images right away, you may visit http://www.lucersoft.com/freeware.php and click on the download link for this program. Lucersoft is the official site for this program...but if you ever need to download from an alternative source, you can. Just google for "LC ISO" to find the many archived freeware sites which mirror this program.

While some people just save ISO files to flash drives, to their hard drive, or to an external drive to make a perfect replica of a CD later for whenever they may need it...other people (like me) will use it extensively with a virtual machine or on their netbook (which normally has no optical disc drive attached to it) whenever they need to have access to the contents of a CD, but do not have a real physical CD-ROM or DVD-ROM drive available to do that.

There are at least three ways that you can read an image file once it is created with LC ISO, PowerISO, or any other program that can create an image file for you:

Method 1: Use a freeware program that we'll refer to hereafter as a "Virtual CD" program. You can get a great free program for this that can mount DVD or CD images (up to 15 at a time!) here: http://www.magiciso.com/tutorials/miso-magicdisc-overview.htm

This type of program lets you mount an ISO file that you created virtually, and make the computer assume it is physical hardware attached to the machine. Virtual CD emulators and similar programs always trick Microsoft Windows into creating a drive letter for a virtual image file by using a special driver that makes Windows believe new hardware has been added, so that you can access your virtual file as if it were a real CD-ROM drive. A logical drive letter is then created and assigned. And as far as Windows is concerned? That program and image file you are using, with this program, are really considered as a "real disc" to it!

As far as programs on your computer are concerned, that virtual drive letter and image file you attached to it are seen as real, too. This is especially useful and even imperative for programs that require a CD or DVD drive to install off of a CD or DVD to work properly.

For programs that normally require you to run them from a disc in order for them to function, you can use a virtual CD drive letter and an ISO image file of an original disc (stored on your computer as a file) and always run them just fine.

Even if you have a physical CD or DVD drive attached to your computer, laptop, or net book...you may still want to use a disc emulator program anyway to access an image file through a virtual drive letter. You may want to do this so that you can (for example) burn a CD or DVD with the physical drive that really is attached to your computer while you use a virtual CD disc emulator to manage and run a program or two from virtual discs that are not (but would normally require that you use one or all of your computer's physical burner drive to run them). By doing things this way, you can burn a disc physically while reading one virtually, and if you want to, you can even make Microsoft Windows think there are two, three, or even four or more physical CD or DVD drives attached to your system if you need to to use that many. Meanwhile, you can keep your real physical drive free for whatever you need to physically read or write media from.

A similar thing can be done with hard drives, and those too are called disk images in the literal sense. That is a topic for another article relative to this one in the future, though. For now, we'll stick to the topic of optical disc emulation, imaging, and retrieval only.

Once you have successfully run a disc emulation program and created or mounted an image file as a drive letter, You should immediately see that a new drive letter available, along with all of the contents of a virtual CD image file when you access that drive letter. On Windows, you can access an image file the same way that you would a regular CD ROM drive or hard drive. You just view and work with it either via My Computer, through Windows Explorer, or you can access it directly through a DOS box by the drive letter the program created for it.

And of course, you can do all of these image file and disc management techniques with Linux and other operating systems, too.

If you are a Linux, FreeBSD, QNX or other UNIX user, you can mount virtual drives the same ways that Windows can with the use of appropriate programs, libraries, and modules to do so. Many UNIX/Linux distributions already have the tools to do this, both from the command line and from any graphical system that might be used such as programs which make use of a graphical front-end like KDE or X11. If you plan to use Linux to mount a virtual CD image, please consult Linux newsgroups, support groups and forums on the web, or if in doubt, visit http://www.linux.org for official distributions and what they carry. I would love to detail that in this article also, but it would further complicate things, especially for intermediate Windows users who would like to create image files and are figuring out these things. Unfortunately Windows help files are not much help when contrasted to UNIX man pages and gnu readme's.

As for DOS users reading this article, you will find further information for dos drivers, TSRs that handle virtual drive mapping, and some of the best freely-available modern-day DOS and DOS-clone support at http://www.freedos.org and mirror sites for the FreeDos distributions.

This concludes the first method and first part of accessing a virtual disc image file. Now, on to method 2...

Method 2: Use 7-zip, Bitzipper, or a similar program. 7-zip is usually the most convenient and easiest to use for reading and creating archives and compressed files and is 100% free. You can obtain it by going to http://www.7-zip.com or by visiting CNET's free download area.

If you don't need to make Microsoft Windows or your current operating system believe that there is a physical CD drive attached to the system through an image file for any reason, then you can use this archive program as a quick and easy solution to read data right out of the image file.

You just click on the ISO file you want to read (or use 7-zip's file manager to navigate to it), double click on it, and then extract any or all files that you need from the image file. It's that easy.

Now 7-zip is only available for windows, so if you need a solution for Mac OS X or Linux, there are free solutions available and alternative freeware archivers that you can download to read ISO files (and some Linux distributions have tools that can automatically read ISO images so you won't even need to look for them if you're fortunate).

This is the most common-sense and fastest method to read a virtual CD image you created from a physical disc if you never need to actually mount it, and don't have to cleverly trick Windows into using the data a certain way.

There's one final way that I'd like to mention though. Many people might already have it on their computer and be using it, too...but not necessarily the way that they can!

Method 3: Use of a virtual machine emulator as a disc emulator. Most emulators such as the freeware VMWare player, Microsoft's freeware Virtual PC 2004 (formerly Connectix Virtual PC as a commercial product), QEMU, and VirtualBox can all mount virtual CD images that are ISO files. You can use the more powerful commercial products like Vmware Workstation or Parallels to mount an image just like the freeware solutions, but you can do more with them usually, and mount more than one at a time. They all basically utilize a virtual operating system platform when they're running (depending what you load on it, it can be Linux, Windows, Mac, Beos, QNX, or other).

Through the virtual operating system and hardware you "virtually" install onto a virtual machine, you can read one or more virtual CD images, and then copy them to and from the host computer (physical machine) to a shared folder or use a file bridge any time you want to at any fashion that works.

An important thing to remember about programs which create CD images is that, unless you tell them not to, they normally do copy everything and all of the CD that they can (including boot information if it is a bootable CD or DVD).

With the exception of a few rare disc types, you will always be able to make perfect 1 to 1 copies and bootable CDs/DVDs from an image file whenever you burn them back to a physical disc as a copy of the original.

One of the rare exceptions to this are the video game CDs and DVDs such as those for PlayStation 2 and PlayStation 3, which read track information differently, and on some consoles may be designed to jump forward over data tracks and have physical differences which make disc replication difficult or impossible through normal means. On karaoke CD+G discs for example, there are no physical disc limitations. But the placement of the data on the disc determines whether a CD+G disc player can read back the data you burned to a CD+G disc correctly, or if it will only play the audio data as you would hear out of a regular compact disc player. This is the reason why karaoke discs do not copy correctly when people try to use traditional CD or DVD burner software to clone them.

Additional copyright protection is in-effect for video games and video karaoke discs. They add even more complications to the copying and imaging process with the hope that they will prevent others from successfully cloning their disc. Generally, there are commercial programs already out there which exist just to defeat such preventions. Some solutions to this may be legal to use, and some may not be. If you do pursue them, you must explore those possibilities at your own risk.

Disc emulation programs can be a fun and educational way to work with media, but more times than not, they are extremely valuable in helping you preserve precious data and preventing media from being destroyed. It also provides numerous ways to access the data the same way in a clever fashion (or faster than possible before when reading from an optical disc).

You can find additional information about disc emulation, image files, and the physical differences and data placement used by different formats if you google things such as the "El Torito bootable CD format", "BartPE", and "live CD". In doing this, you will find out even more about virtual discs and how CDs and DVD-ROM drives work. Beyond that, you'll also find valuable source code for programmers and many other alternative programs that could be used in this article, but were not for the sake of keeping consistency in using a combination of programs that are always guaranteed to work for the reader should you want to try them on a common system. There are plenty of methods that will work for this. If you have time and wish to experiment, then by all means! You may even discover a 4th or 5th way to access an image file as you do so that I hadn't yet realized. I wish you the very best of luck, want to thank you for reading this article, and of course...happy imaging!