This article is the second in a five-part educational series on laboratory data processing and computers. The authors describe the major components of peripheral storage and the limitations of input/output devices, and analyze in terms of laboratory workflow the type and placement of input/output devices. Preceding the article are competency areas and performance objectives, defined by the Laboratory Computer Applications and Data Processing Committee. Following the article are questions with which readers can test their understanding of the material. Next month the authors will focus on software.