appliance vs what’s under the hood

appliance

noun
  • An attachment, a piece of equipment to adapt another tool or machine to a specific purpose. 

  • An implement, an instrument or apparatus designed (or at least used) as a means to a specific end, especially 

  • A non-manual apparatus or device, powered electrically or by another small motor, used in homes to perform domestic functions (household appliance) and/or in offices. 

what’s under the hood

How often have the words appliance and what’s under the hood occurred in a corpus of books? (source: Google Ngram Viewer )