scratchpad vs sketchbook

scratchpad

noun
  • A pad of paper for preliminary notes or sketches or writings, etc. 

  • A piece of temporary memory to hold details of a current conversation, usually scratchpad memory. 

sketchbook

noun
  • A book or pad with blank pages for sketching; a sketch pad. 

  • A book of printed sketches. 

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