Found to be helpful from a different thread......
Stujoe says:
Aren't the User Interfaces quite different? I would think the most immediate way to tell is from the difference between a first and second generation is in the home screens. The Text Links at the top are different. The First gen starts with Newsstand and the Second Gen starts with Shop.
So, I would say:
1. Go to the Home Screen. Look in the Upper Left.
1a. If the First Link is Newsstand, you have a First Generation and you can stop there.
1b. If the First Link is Shop, you have a Second Generation. Proceed to 2.
2. If it is a Second Generation, look for the Volume Control buttons.
2a. If it has Volume Control Buttons, you have a Second Generation HD.
2b. If it doesn't have Volume Control Buttons, you have a Second Generation non-HD.
Does that sound right?
Amazon.com: Customer Discussions: Kindle Fire - Which do I have?