Just the other day a friend called to ask me a bunch of questions about some files he'd downloaded using Bittorrent. It didn't bother me in the least to answer his questions, but about halfway through our discussion a thought struck me: I've done my faithful jimcofer.com readers a grave disservice. Sort of like a parent that gives their kid the keys but doesn't teach him how to drive, I realized that I had given you all the information you need to download files from Bittorrent, Usenet, P2P apps and IRC (collectively known throughout the rest of this article as "Darknet") but had not told you exactly what you were going to be downloading! Although small items like an MP3 track might be transferred "as is", many of the larger items available for download - like movies and software applications - come "packaged" in many formats and compression schemes. Downloading most things isn't as simple as clicking on a link, waiting for the download to complete and clicking on a song, movie or SETUP.EXE file. This article will tell you about the most popular Darknet file formats and teach you how to deal with the mind-numbing array of things that might appear in your downloads folder.  

We'll begin with the ZIP format.  ZIP is far and away the most widely used compression scheme in the Windows world. There are literally millions of legitimate ZIP files available for download from the Internet, from driver updates to software patches to shareware programs. You've probably even used ZIP to email Word or Excel documents to coworkers. ZIP has become so ubiquitous that Windows XP even has a built-in utility to unpack ZIP files! While ZIP was originally developed to save disk space and bandwidth - like most other compression schemes - many people use ZIP files to send items that cannot be compressed - like pictures and MP3s - because it's handy to have a single archive "package". After all, who wants to attach 27 individual pictures to an email when you can just "zip" them up and email a single file? Having said all this, the ZIP format has one tragic limitation - to be discussed in the next section - that keeps it from being used very much in the world of Darknet. Therefore in Darknet you will typically only see ZIP used for small files of 10MB or less. To unpack your files, just right-click on the file and select "Extract Files" (using Windows XP's built-in extractor) or "Winzip > Extract To..." (if using WinZip, the most popular full-featured ZIP program for Windows).

RAR is the undisputed "King of the Hill" in the Darknet world. The overwhelming majority of the files you download from Usenet, Bittorrent and IRC are compressed using this format. There are several reasons why RAR beat out ZIP to become the file trading format of choice: RAR has many specialized "modes" for archive creation, has the ability to repair damaged archives, supports Unicode to process non-European file names, supports strong encryption and has software available for every version of Windows not to mention Mac OS X, DOS, OS/2, Linux, FreeBSD, OpenBSD, NetBSD, Amiga OS, Solaris 8 Sparc, Solaris Intel, AIX, IRX, BeOS and QNX6. But the main reason that RAR was chosen for use on Darknet is that it supports spanning. This means that you can easily break up an archive into smaller parts. For example, if you have 200MB of documents that would normally compress into a single 100MB RAR file, you have the option of breaking the archive into ten 10MB files or four 25MB files or twenty-five 4MB files or fifty 2MB files or.... well, you get the idea. The advantage of breaking up archives into smaller parts is obvious - if you lose your Internet connection during a 100MB download, it's far better to have to resume your download at part six of ten than resume it all over again from the beginning!

RAR archives typically look like this:

Spiderman2.part01.rar
Spiderman2.part02.rar
Spiderman2.part03.rar   <-- These files were created with newer versions of WinRAR
Spiderman2.part04.rar
Spiderman2.part05.rar

If your files look like the first example, all you need to do to extract these files is to right-click on any file in list and select "WinRAR > Extract Here" or "WinRAR > Extract to [subfolder]". The difference between these two options is that the first one will unpack the files to the current directory while the second one will extract them to a new subfolder in the current directory. There is also "WinRAR > Extract to..." which will open a save dialog box that lets you choose any location on your PC.

If your files look like the second example, right-click the "main" file (the one with the extension "RAR") and select any of the options listed above. Also note that there's no requirement that there be a *.RAR file - old school RAR archives can (but rarely) begin with a R01 or R00 file.

To unpack RAR files, install a program like WinRAR.

ACE files were once quite popular with the multimedia crowd as ACE claims to have better compression for media that is inherently compressed - namely movies, images and music. Although ACE files are more rare than they used to be, they're still out there in small numbers. The good news about ACE files is that WinRAR can extract ACE and ZIP files in addition to its own RAR format. Even better news is that ACE files work exactly like "old version" RAR files, except that the main file has the extension *.ACE and any subsequent files will be named *.A00, *.A01, *.A02, etc. - so just right-click on the *.ACE file and choose one of the "WinRAR > " options listed in the section above to extract. 

In the past couple of years, the use of disc images as a way of distributing software has been rapidly gaining in popularity. A disc image is essentially nothing more than a huge ZIP-type file that contains the disc's contents plus extra information about the disc, such as the disc's name and directory structure. There are several programs - indeed, even several types of programs - that can create disc images but they all basically work the same way - someone puts a CD or DVD into an optical drive and the program then copies the contents of the disc to a single file. You - the end user - then download the image file and use CD burning software to burn the image to a blank disc. Or better yet, you can use a virtual drive to mount the image and skip the burning process altogether. But I'm getting ahead of myself here.

The case for using disk images is quite clear - they allow the end user to download a single file and create as many copies of a disc as he or she needs. Most versions of the Linux operating system have been distributed this way for ages and even Microsoft has gotten in on the disc image game - as a longtime MS beta tester I remember back when they would send you test (beta) versions of their software on CD-ROM... Nowadays they just have a secure website where testers can download disc images of their latest and greatest. I remember testing Windows XP - Windows Whistler it was called at the time - and downloading several versions of the OS. I'd download a single file and when I was ready to create a CD-ROM of it, I'd open Nero and select File > Burn Image and in a few minutes I had a fully-functional Windows XP CD-ROM.

Disc images are typically used on Darknet for "large" software releases like operating systems, office suites and DVD video. As a general rule, if the software is large enough to require a full disc, it will be distributed via disc image. Unfortunately, there are many different types of disc image:

ISO - This is the original disc image file. "ISO" is short for "ISO 9660" which is a standard for disc images. Any software that can burn any disc images should be able to burn an ISO image. ISO files are typically used for data discs only, as the ISO format cannot create an image of an audio CD.

BIN\CUE - This image type is composed of two parts: a large BIN (binary) file that actually contains all the disc data and a small CUE file that tells your burning software what type of data the BIN contains and where to put it on a disc. This format was made popular by the once popular CDRWin burning software. Of course, CDRWin can burn these images, but Nero and Alcohol 120% can burn them as well. Used for CD-ROM, DVD and audio CDs.

IMG - This image type was made popular by DVD Decrypter, a popular freeware program for copying DVD videos to your PC. In fact, if you have DVD Decrypter installed on your system, all you need to do is insert a blank DVD into your burner and right-click on the IMG file and select "Burn with DVD Decrypter". As you might guess, this format is restricted to DVD video only. As far as I know, only DVD Decrypter burns these images. 

MDS - This is an image created with Alcohol 120%. Alcohol has become insanely popular for its ability to burn images of copy-protected game discs. It doesn't matter if the CD is protected with SafeDisc or SecureROM or what have you - Alcohol can burn it! But Alcohol is more than a burning program - perhaps my favorite feature of the software is its "virtual drive" feature. Alcohol can install one (or more) "virtual" CD\DVD drives on your system. Windows will treat these virtual drives just like new physical optical drives in your system. To mount images on the virtual drives, you just right-click on the drive and select "Mount Image", then choose the ISO, BIN\CUE or MDS file in question. Windows will then act just as if you opened a physical drive and inserted a disc. This is cool on so many levels - aside from saving you the hassle of actually burning the images to disc, using virtual drives to install software is much faster than swapping out CD-ROMs. Gamers also like virtual drives because image files on hard drives are much faster than CD-ROM discs. Alcohol 120% can read just about every image file type mentioned on this page too! It's easily my favorite disc imaging program! Also, note that MDS images can also be read by BlindWrite.

NRG - This is a Nero disc image. When you install the Nero burning software, you will have an available CD-burner called "Image Recorder". If you choose "Copy DIsc" and choose "Image Recorder" as your burner you will get an NRG file for your efforts. Perhaps because Nero is so popular with the geek set, some third-party apps - like Alcohol 120% - can read\burn NRG images as well.

CIF - This is a Roxio disc image. It is created the same way as a Nero image, only it's created by Roxio's Easy CD Creator (or, as the new versions are called, "Easy Media Creator"). Because "Easy Creator" is *not* popular with geeks, there are no third-party programs that can burn or read CIF files - as far as I know. 

CCD - Before there was Alcohol 120%, there was CloneCD. CloneCD was legendary "back in the day" for being able to make bit-by-bit copies of CD-ROM discs, regardless of their protection scheme. Unfortunately, the company that created CloneCD was pressured to stop production of the software by the German government. Images created by CloneCD can be read by CloneCD,  Alcohol 120% and BlindWrite. You can download the final version of CloneCD from Old Version.

CDI - An image created by the DiscJuggler program, which was similar to, but less popular than, CloneCD. These images can be read by DiscJuggler and Alcohol 120%.

BWT - An image created by the BlindWrite program, which is similar to, but less popular than, Alcohol 120%. These images can be read by BlindWrite and Alcohol 120%.

One last word about disc images: if you *do* burn them to disc, make sure you burn them properly! In modern versions of Nero, you burn an image by clicking on Recorder > Burn Image. If you try to burn a disc image the "traditional way" - that is, clicking on New > Data CD-ROM and dragging and dropping the image file onto the CD-ROM layout - you will end up with a CD-ROM that contains the actual disc image file and not the image file's contents. In other words, if you drag and drop OFFICE2003.ISO onto a standard CD-ROM layout you will get a CD-ROM with... OFFICE2003.ISO on it. If you click on Recorder > Burn Image and then point Nero to the OFFICE2003.ISO file, you will get the CD you actually want. Having said that, there is something to be said for burning disc image files to DVD. If you have a game that has 4 disc image files, you can easily burn the CD images to DVD and then use virtual drives to mount and install the game from DVD.