CPU vs mainframe

CPU

noun
  • The main computer case containing the central components of a personal computer. 

  • Any character or entity controlled by the game software. 

mainframe

noun
  • A large, powerful computer able to manage very many simultaneous tasks and communicate with very many connected terminals; used by large, complex organizations (such as banks and supermarkets) where continuously sustained operation is vital. 

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