The document discusses the different types of information systems and provides examples of the information systems used by four major tech companies: Amazon, Apple, Facebook, and Google. It describes the four main types of information systems as transaction processing systems, customer relationship management systems, business intelligence systems, and knowledge management systems. It then provides details about the specific industries each company serves, their revenue models, and examples of information systems they use, such as transaction processing, customer relationship management, business intelligence, knowledge management, and other systems.