Fast forward 20 some odd years. I got my first PDA (no, not Public Display of Affection, I am a techie, I didn't even know that meaning until someone told me about it. I am talking about a Personal Digital Assistant) I had a PalmPilot IIIxe.I tinkered and toyed with getting my books onto this device and found a few things that worked but nowadays there are a vast jungle of options for reading books digitally.
When you go down to the store to buy a new appliance, you never stop to think about whether it will work with your electricity at home. Why not? There are different ways electricity can be delivered and if you have traveled out of the United States, you know that plugs aren't the same everywhere in the world. Why don't we worry? Because of standardization. Someone somewhere (or probably a group of someone's in a meeting) decided that one style of plug was going to be required either by law or by consensus. This is slowly happening with cell phone adapters, among other things.
It however hasn't happened with books. Why does that matter? Well, if you are deciding on a device that is dedicated to reading books, or you are decided to buy books that you want to use with multiple devices it's worthwhile to know what you are looking at it. With books, there are still a bunch of different widely adopted formats of eBooks. Below are three and where you are most likely to encounter them.
This is the file format for the Amazon Kindle. You probably won't ever see it because if you have a Kindle your books are delivered via Cell phone or Wi-Fi and they live on Amazon.com and your device. But it's good to know it exists. Also, since Amazon is interested in selling books, the software needed to read the .azw format is widely available on multiple platforms.
This is the format of choice for iBooks on the iPad, iPhone and iPod Touch. It is an open format that while a little heavy on resource use, it is still a very good format that is being supported. The fact that it is the format chosen for the iBooks app means that it will be strong for as log as Apple is strong and supports it.
These two file formats are variations of each other. The .prc format was created for the Palm™ devices. MobiPocket is a reader you can still use on many portable devices and the .mobi format is still commonly used.
To learn more you can start with the really great wikipedia article on eBook formats: http://en.wikipedia.org/wiki/Comparison_of_e-book_formats