An American Editor

October 27, 2010

An eBook Primer: Part II

Yesterday’s article, An eBook Primer: Part I, explored ebooks and ereaders in general. Today’s addresses the issue of ebook formats. Today’s article first appeared on Teleread‘s website and was written by a Teleread staffer. The article is reprinted with permission from Teleread and is copyright 2010 by North American Publishing Company, the parent of Teleread. To reprint the article, please contact Teleread.

Future instalments of the “primer” will also be reprinted. I hope you find them valuable and informative.


TeleRead E-book Primer Part Two: Formats

By Chris Meadows

Ebooks_stack_lg You may be old enough to remember a time when there were two different formats of video tape–VHS or Betamax. If not, you’re almost certainly old enough to remember that there were two different competing high-definition DVD formats a couple of years ago–HD-DVD and Blu-Ray.

And you’ll know that in both cases, you had to have the right player to play each format: Beta tapes would only play in Beta players, VHS tapes would only work in VHS.

It’s much the same way with e-books, except that instead of only two competing formats, there are at least a dozen. Fortunately, only three of those really qualify as important enough to worry about right now, or else this article would be a whole lot longer!

 File Format vs. DRM Format

E-books actually have two different types of format: file format and DRM format.

File format is like what we’ve talked about above—the different ways to put e-book files together developed by different companies, kind of like the difference between VHS and Beta. The main e-book file formats I will be talking about today are PDF, MobiPocket/Kindle, and EPUB. Some e-book readers will read only one kind of file format, while others will read several.

DRM format has to do with Digital Rights Management, which is a kind of lock that some companies put on their e-books to prevent buyers from copying them and passing them on for free—or reading them in a competitor’s e-book device.

Not all e-books will have DRM, but most of the ones you buy from big e-book stores such as Amazon or Barnes & Noble do. Some e-book formats can have different forms of DRM applied to them, depending on which store you buy from. (For more information on DRM, see the TeleRead DRM Primer.)

If you want to read an e-book, your e-book reader device or application must be compatible with both the file format and the DRM format of the e-book.

The only e-book readers that can read files in multiple competing file and DRM formats are the iPhone, iPod Touch, and iPad, simply because they can run reader apps from all the different companies.

The interaction of these two different kinds of format, and the restrictions on what kind of readers can read both of them, is what has made the e-book market so complicated for first-time buyers. (It is also why the Kindle is such a popular reader—when Kindle owners buy e-books from Amazon, they just work without all that confusion.) The reason I’m writing these primers is to try to simplify some of that.

There are far, far more e-book reading devices available than just the Kindle, Nook, and Sony. There are readers from brands you’ve never heard of, far far more than I will be able to cover in these primers. If you want to know whether you can read an e-book with your device, you need to find out what formats the e-book is in, and what formats your device can read.

A great place to find out more about e-book formats is the MobileRead wiki’s e-book formats page.

PDF Format

Adobe’s PDF (Portable Document Format) files have been in use for a long, long time. They allow book and document producers to standardize the appearance of printable files, so they can be sure the files will look exactly the same no matter where or how they’re printed out. This is especially useful for paperwork, such as forms that must be filled out.

They are also used for e-books, especially in the role-playing game industry, for the way they can exactly represent the printed page on a computer screen. This is useful for books that have a lot of specific formatting (such as the charts and tables from role-playing games) or otherwise just need to look nice.

While the 8.5″ x 11″ form factor of most PDFs means they’re not ideal for reading on most computer screens, they’re still better than nothing. The form factor also means they often look cramped on smaller e-book reader screens. This is why most e-books are sold in other formats, and if another format is available you would probably be better advised to get it than to get PDF.

Popular e-book readers with some PDF compatibility include the Kindle, the Sony Reader, and the Kobo Reader. Computer programs that read PDFs include Adobe Reader and Adobe Digital Editions (for DRM-protected PDFs). There are also PDF readers for the iPhone and iPad’s iOS, such as GoodReader and Dicebook. Their larger screen size means that PDFs often look best on the iPad or the Kindle DX.


Some PDF files have Adobe’s Adept DRM on them, which means they have to be read on Adobe Digital Editions. Most PDFs are not DRM-protected, however.

MobiPocket/Kindle Format

It might surprise you to know that the super-modern up-to-date Kindle actually uses one of the oldest e-book formats still in continuous use. This format started out as a modification of the PalmDOC format for Palm Reader, to allow HTML-like text emphasis and other tagging. It was used in MobiPocket Reader for the Palm PDA, later expanding to other PDA platforms, until Amazon purchased the company several years ago.

Subsequently, Amazon made some changes to the format and now uses it in the Kindle. The biggest change is that the Kindle uses an entirely new, incompatible DRM scheme from the original MobiPocket DRM (see below).

MobiPocket format is often referred to as PRC or MOBI format based on its file extensions—especially in the tech specs of compatible e-book readers. (It’s actually erroneous to call it PRC, because PRC was a container file format that could have contained any of a number of different Palm database files. However, since almost nobody else uses the original Palm formats anymore, most .PRC files encountered these days will be MobiPocket.) Kindle format is sometimes called AZW.

There are official MobiPocket reader apps for the PC, Palm, Blackberry, and Windows Mobile. DRM-free MobiPocket files can be read by a number of other apps for PC, Apple, or iOS, including Calibre, Stanza, and FBReader. However, there is no app for iOS that can read MobiPocket-encrypted e-books.

The Kindle can read DRM-free MobiPocket books (such as the ones Baen has available on its Free Library and Webscriptions), but not e-books with the original MobiPocket DRM on them. Likewise, DRM-protected Kindle e-books cannot be read on any of the MobiPocket readers, though there are Kindle Reader applications that read Kindle books for a number of different platforms including PC, Android, and iOS.

MobiPocket/Kindle and DRM

The original MobiPocket DRM format was one of the most widely-used formats for selling e-books in the days before the Kindle, on stores such as Fictionwise, eReader, BooksOnBoard,, and others. However, none of these books can be read on the Kindle without first cracking the DRM (which is illegal under current US copyright law).

The Kindle DRM format is used for the Kindle and its related readers. As mentioned above, it can be read by the Kindle and Kindle Reader software, but not by anything else.

EPUB Format

EPUB has come to be considered more or less the “standard” e-book format of the publishing industry. It is the main e-book format currently used by Sony Reader, Adobe’s Nook, Borders’s Kobo Reader, Apple’s iBooks, Adobe Digital Editions, and a number of other reader devices and applications. Most e-books you can buy now (from anyone except Amazon) will come in EPUB format of some kind. About the only e-book device that won’t read EPUB is the Amazon Kindle.

However, even this “standard” has problems; it is saddled with no fewer than three competing DRM formats, meaning that if you bought the e-book from a store that uses DRM, odds are you’ll only be able to read it on devices or programs that work with that particular store.


There are three different DRM formats for use with EPUB:

Adobe Adept is the first DRM format, and the one used by Adobe Digital Editions, Barnes & Noble’s Nook, the Sony Reader, and the Kobo Reader, as well as a number of lesser-known e-book devices.

Barnes & Noble’s Nook/eReader DRM uses the DRM that was originally developed by the eReader e-book store for use on its own special e-book file format (later bought by Barnes & Noble just as MobiPocket was bought by Amazon). As noted above, it can also read titles in Adobe’s Adept DRM.

The iBookstore uses the same Fairplay DRM that Apple used on music and currently uses on movies and iOS applications.

Except that the Nook can also read Adept, e-books sold in each of these DRM formats are entirely incompatible with readers that use the other two formats (though DRM-free EPUB books, such as those sold by Baen, can be read by all three). If you buy a DRM-locked EPUB book from the iBookstore, you can’t read it on the Nook or the Kobo, for example.

Other Formats

The above formats are the main formats currently used by the “top five” e-book devices or applications, and hence the ones you’re most likely to encounter if you buy any well-known e-book device or app: Kindle, Nook, Sony, Kobo, or iPad/iPhone. There are a number of other formats that are still in some limited use, such as eReader or Microsoft Reader (LIT), but it is rare for anyone using one of the major e-book reading devices or apps to encounter them anymore (and this primer is complicated enough already!). At present, PDF, MobiPocket/Amazon, and EPUB are the main ones to worry about.




  1. […] Feeling overwhelmed by all the ebook reader choices out there? Check out the ebook primer at An American Editor to help you figure out what sort of reader to buy: Part 1 and Part 2. […]


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