The II Plus had the so-called "Autostart ROMs", meaning that it will attempt to boot from disk on power-up. If no system disk is present, Drive 0 will spin endlessly until the user presses Reset (or Ctrl+Reset on machines with the Ctrl+Reset safety switch enabled) to enter Applesoft BASIC.
The II Plus had special ROMs that automatically tried to boot from a disk when powered on. If no disk was found, Drive 0 would spin endlessly until the user pressed Reset (or Ctrl+Reset if available). This allowed users to access Applesoft BASIC.