RMAN backup doubt

I have this RMAN backup and I dont understand why the delete and backup current controlfile sentences dont have "device type disk" and the others do have it.
run{
configure retention policy to recovery window of 6 days;

backup current controlfile;

sql 'alter system switch logfile';

backup device type disk database;

backup device type disk archivelog all;

crosscheck backup;

delete noprompt expired;

report obsolete;

delete noprompt obsolete;

crosscheck archivelog all;

delete noprompt expired archivelog all;
}

Thank you very much.

Thank you very much.