memory stick vs pen drive

memory stick

noun
  • A portable solid-state electronic flash memory data storage device equipped with a USB (or similarly specified) plug for direct connection to a corresponding port; a USB drive, thumb drive or pen drive. 

  • One of a series of memory devices manufactured by the Sony Corporation ranging in size from a USB drive down to a flash card. 

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 memory stick and pen drive occurred in a corpus of books? (source: Google Ngram Viewer )