PDA stands for Personal Digital Assistant. It refers to a small portable computer that supports database objects to serve as a handy reference for the user. These typically include a calender, a todo list, an address book, and a memo pad. More powerful PDAs include the ability to augment the included Personal Information Management, PIM, capability with built-in and third-party programs.
A modern PDA will use computer hardware (usually ARM based) coupled with a color touch screen, memory and sometimes other specialized hardware. It will typically run one of the following OSs: Windows Mobile, PalmOS, Symbian OS (A replacement for EPOC), BlackBerry, or Linux. In some cases a PDA functionality will be built into a cell-phone called a smartphone. The smartphone will often have a smaller screen which may not be a touch screen.
The main features of a PDA include its versatility in doing several things and its portability. It is often intended to be an extension of your desktop or laptop computer and will thus sync information between your main computer and the PDA. In some cases it may have WiFi and/or Bluetooth support and will often have a web browser built-in as well. A PDA can usually play music and audio books and may even have a microphone for note taking.
For a list of PDA's that are deemed suitable for eBook Reading see: PDA devices
As portable computer based solutions appeared in the 90s the idea of reading a book on a computer began to take form. Apple coined the term PDA to stand for Personal Data Assistant with the introduction of the Newton in 1992. The acronym stuck but the D came to mean Digital rather than Data. Early Palmtop portable solutions were developed by Psion and Hewlett Packard using 8086 type processors.
The problem with these early units was that they were intended to replace the main computer but they did not interact with your home computer very well. Palm had the idea that a PDA should supplement, not replace, your home computer. Palm launched the PDA revolution with its Palm Pilot in 1996. It was designed from the beginning to sync data between your handheld and your home computer thus providing you with data you needed from your computer while you were mobile. The term PIM, personal information management, was coined to identify the address book, appointment data, and todo lists as items you might needed with you. This plus a few notes became indispensable items to have in your pocket.
Initially an eBook reader was an add-on to palmtop and PDA solutions. The PalmDoc format for eBooks appeared in late 1996 with eBooks in 1997. This helped lead the Palm to its early prominence. Microsoft started their own WinCE OS in 1996, initially for Palmtop computers and the PocketPC emerged in 2000. Microsoft Reader was developed for the PocketPC.
 PDA FAQs for eBook use
 Can I use my PDA as an eBook reader?
Yes, you can. This is one of the great uses for a PDA. You can hold a full library of books on an SD card and reading is easy with the unit in the palm of your hand. All you need is a program to read the eBooks and a source of books. See eBook Stores. Most of the classics are freely available while more recent books can be purchased. One of the complications with eBooks is that they are often formatted and designed for a particular eBook reader so you will need to have an appropriate reader to use with the book. For Pocket PC PDAs there are 5 main readers. These include Microsoft Reader, Palm eReader, Adobe Reader, MobiPocket Reader, and Tome Raider. Palm users will find all of the readers mentioned above except the Microsoft Reader. There are many other readers and eBook formats for PDAs but these are the main ones.
Note that eBooks have two basic flavors in addition to multiple formats. There are free eBooks and books you have to pay for. Some of the time the books you have to pay for are locked and must be unlocked to be read using a key supplied by the company you buy the eBook from. The readers mentioned above have support for locked books, called DRM (digital rights management) in the trade. In some cases a DRM book is locked to the reader and platform but other DRM solutions ignore the platform or allow a fixed number of platforms such as 4. Most of the DRM books cannot be printed since printing is a way to convert a file to a different format and break DRM.
 Why do I need a special reader to read eBooks?
Actually you may be able to read many eBooks without a special reader. Project Gutenberg releases all of its books in .txt format for simple reading using a text editor. (They also release some books in other formats.) For Pocket PC this means these files can be easily read by Pocket Word. However, an editor is likely not the best tool to read books with. It is typically not oriented toward just reading a page at a time and does not support such features as bookmarking your progress. It is also easy to accidentally modify a book you are trying to read with an editor. You can set the file to read only to prevent saving accidental modification. In addition .txt file books do not lend themselves to elaborate or easy to read formatting options. They often have fix length lines of data that do not wrap well on the PPC screen or require scrolling. In addition there is no DRM protection possible for these kinds of books and no graphics support.
The advantage of using a dedicated reader program is that it won't accidentally modify the file. These programs also feature easier methods to page through the file and some can even directly read files that have been compressed using zip. For a better reading experience you may want to convert text files to one of the other formats available.
 What is the difference in dedicated hardware vs. PDA?
A PDA and a dedicated eBook reader both offer a portable solution for reading eBooks but they have a very different approach. A PDA is a general purpose unit with good performance and is generally small enough to fit in your pocket while an eBook reader is simplified for one purpose, has a larger screen (5 inches or larger vs. approximately 3.5 inches diagonal), and longer battery life. To achieve these features an eBook reader generally uses a slower processor and gives up color display, touch screens, low powered or even no backlight, and performance. Both will generally offer the ability to play mp3 files as well although a PDA will generally offer more options and may even support video. A dedicated eBook reader may support images but generally these are displayed gray scale monochrome and may be limited to only 4 levels of gray. Color displays and backlights are big battery hogs.
An eBook reader is optimized for reading enjoyment and will likely offer higher resolution displays with large full page displays from 5 inches up to more than 8 inches mimicking a paper book. The latest technologies even have a paper look and don't need any battery power until you turn the page. However, there are some eBook features that may be available in a PDA that are missing in a dedicated reader. For example the ability add annotation or being able to write on the pages themselves such as drawing a circle for review purposes. Highlighting is also available on many PDA versions but is seldom available on dedicated readers. PDAs can also be used to read more eBook formats and some eBook formats are not available on any dedicated reader. This means that more eBooks are available for PDAs. It is also true that some formats are only available for a particular eBook reader.