Hard Drive Sizes

• If you are specifically looking for an iPod touch with a 16GB hard drive, you will want to purchase a first- or second-generation iPod touch. Both of these models were offered in 8GB, 16GB or 32GB models. Apple dropped the smaller hard drive sizes with the release of the third-generation, offering only a 32GB and 64GB hard drive. The fourth-generation release saw a return of the 8BG model in addition to the 32GB and 64GB.
  
  

Physical Design: First Generation Vs. Second Generation

• The first- and second-generation iPod touch models saw a design upgrade. The second-generation models are identified by a more contoured design and an oval shaped antenna on the back.
  
  

Software: First Generation Vs. Second Generation

• If you own the 16GB first generation iPod touch, you will be unable to upgrade at iOS 4. Second-generation iPod touches can upgrade to iOS 4 software, however the features are limited to only the home screen folders, unified inbox and threading for emails, GameCenter and AirPlay.
  
  

Cameras

• The first- and second-generation iPod touches did not include cameras. If you are looking to purchase an iPod touch with a camera, you will need to purchase a fourth-generation iPod touch or later.