1. Folks consider adb sideload <ZIP> when they have a ready to flash .zip file. The command is mostly used when booted into Recovery mode.

Fastboot on the other hand often deals with per partition flashing at a time. E.g. fastboot flash recovery <IMG> -- only flashes Recovery partition and not all the relevant partitions for ROM installation. ADB sideload <ZIP> usually does full ROM installation in one go.

2. You unlock the bootloader only if it is locked. Google Nexus devices comes with locked bootloaders while some Chinese Mediatek devices comes unlocked. You've to search web for your model.

3. No, the command doesn't work on every Android device. The reason is 2.

1. Folks consider adb sideload <ZIP> when they have a ready to flash .zip file. The command is mostly used when booted into Recovery mode.

   Fastboot on the other hand often deals with per partition flashing at a time. E.g. fastboot flash recovery <IMG> -- only flashes Recovery partition and not all the relevant partitions for ROM installation. ADB sideload <ZIP> usually does full ROM installation in one go.

2. You unlock the bootloader only if it is locked. Google Nexus devices comes with locked bootloaders while some Chinese Mediatek devices comes unlocked. You've to search web for your model.

3. No, the command doesn't work on every Android device. The reason is 2.

1. Folks consider adb sideload <ZIP> when they have a ready to flash .zip file. The command is mostly used when booted into Recovery mode.

Fastboot on the other hand deals with per partition flashing at a time. E.g. fastboot flash recovery <IMG> -- only flashes Recovery partition and not all the relevant partitions for ROM installation. ADB sideload <ZIP> on the other hand can achieve full ROM installation in one go.

2. You unlock the bootloader only if it is locked. Google Nexus devices comes with locked bootloaders while some Chinese Mediatek devices comes unlocked. You've to search web for your model.

3. No, the command doesn't work on every Android device. The reason is 2.

1. Folks consider adb sideload <ZIP> when they have a ready to flash .zip file. The command is mostly used when booted into Recovery mode.

Fastboot on the other hand often deals with per partition flashing at a time. E.g. fastboot flash recovery <IMG> -- only flashes Recovery partition and not all the relevant partitions for ROM installation. ADB sideload <ZIP> usually does full ROM installation in one go.

2. You unlock the bootloader only if it is locked. Google Nexus devices comes with locked bootloaders while some Chinese Mediatek devices comes unlocked. You've to search web for your model.

3. No, the command doesn't work on every Android device. The reason is 2.