Android 1.0 marked the beginning of the Android journey, and it paved the way for future versions of the OS. The release of Android 1.0:
A 6.3 MB set of Java class libraries—significantly smaller than modern versions—providing the APIs for app interaction. System Apps: android 1.0 rom
Yes, you can still run Android 1.0 — mostly on emulators or old hardware. Android 1