From 1.0 to 2.0, the Initial journey

2.2 Or Froyo, a Major Improvement
Froyo brought major changes in the way the Android operating system worked. Almost everything was revamped in this update and Android became a powerful and user friendly OS. Froyo increased general speed of the Android devices by revamping the UI response time and the hardware interaction. USB tethering, Adobe Flash support and installing applications on removable media were the major upgrades over the Éclair. Currently, this is the most popular Android version that can be found on most phones.
To Know more about android versions....