The OS was built for a world where a 528 MHz processor and 192 MB of RAM were cutting-edge. Today, your smartwatch likely has ten times that power.
If a modern user were to flash an Android 1.0 ROM onto a device today, they would find an operating system that feels instantly familiar yet startlingly primitive. It was known internally at Google as "Base." The interface was a stark departure from the grid-of-icons approach popularized by the iPhone. android 1.0 rom