It’s hard to imagine, but multitasking as we know it didn’t exist until the introduction of iOS 4. Multitasking back in the day was very limited, and it was an iPhone 4 exclusive feature, despite the fact that the iPhone 3G and the second-generation iPod touch also used iOS 4.
This feature lets you quickly switch between apps by double-pressing the Home button. Additionally, you could do things like continue playing music even if you exited the app. You could also leave other apps open in the background while using a new app. Back in the day, this technology was basically groundbreaking.