Back in the day, Android phones would take a minute or two to start up after a shutdown. That's partly why they took so long to boot, but the Android's boot system itself was poorly designed and optimized. Even in the early versions of the iPhone, the boot times were way faster than Android phones. Starting with Android Oreo (version 8), the operating system switched to a faster decompression algorithm (LZ4), which allowed the bootloader to unpack the kernel faster. That's because they save the system state in memory, so the operating system doesn't have to fully re-initialize on a reboot.