This paper surveys how the computer input/output (I/O) subsystem is taught in introductory undergraduate courses. It is important to study the educational process of the computer I/O subsystem because, in the curricula recommendations, it is considered a core topic in the area of knowledge of computer architecture and organization (CAO). It is also a basic knowledge to be acquired in order to work in areas such as human-computer interaction (HCI) or embedded systems. Examination questions, course syllabi, and textbooks were analyzed to identify which teaching approaches are being used. Individuals teaching the I/O subsystem could choose between the options explained here, according to their intended learning outcomes. In addition, a literature survey was conducted on the development and use of tools to improve student understanding of I/O and to make the topic less abstract and more attractive. A goal is to indicate to computing education researchers that the majority of the literature reports experiences in developing or using different resources or educational methodologies, but that these are not based on a theory of learning.