clipboard vs strongbox

clipboard

noun
  • A flat piece of rigid material, such as card or plastic, with a clip at one end under which papers can be held. 

  • A buffer in memory where the user can store data temporarily while transferring it from one place within an application to another or between applications. 

strongbox

noun
  • A sturdy box with a lock for storing valuables. 

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