flashcard vs pen drive

flashcard

noun
  • A solid-state digital memory storage format, commonly found on computers, digital cameras and cellphones. 

  • A card used to aid rote memorization. One side of the card contains data of one kind, or a question, and the other side contains the associated response which one wants to memorize. For example, one side could contain an English word, and the other side the Spanish translation. 

pen drive

noun
  • A small electronic device used to store digital data, more portable and robust than a hard drive; a flash drive. 

How often have the words flashcard and pen drive occurred in a corpus of books? (source: Google Ngram Viewer )