disk-on-key vs memory stick

disk-on-key

memory stick

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

  • 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. 

How often have the words disk-on-key and memory stick occurred in a corpus of books? (source: Google Ngram Viewer )