Computer systems have long been seen as more than just mechanical systems (Boulding, 1956). They seem to be systems in a general sense (Churchman, 1979), with system elements, like a boundary, common to other systems (Whitworth & Zaic, 2003). A computer system of chips and circuits is also a software system of information exchanges. Today, the system is also the human-computer combination (Alter, 1999); for example, a plane is mechanical, its computer controls are informational, but the plane plus pilot is also a system: a human-computer system. Human-computer interaction (HCI) sees computers as more than just technology (hardware and software). Computing has reinvented itself each decade or so, from hardware in the 1950s and 1960s, to commercial information processors in the 1970s, to personal computers in the 1980s, to computers as communication tools in the 1990s. At each stage, system performance increased. This decade seems to be that of social computing, in which software serves not just people but society, and systems like e-mail, chat rooms, and bulletin boards have a social level. Human-factors research has expanded from computer usability (individual), to computer-mediated communication (largely dyads), to virtual communities (social groups). The infrastructure is technology, but the overall system is personal and social, with all that implies. Do social systems mediated by technology differ from those mediated by the natural world? The means of interaction, a computer network, is virtual, but the people involved are real. One can be as upset by an e-mail as by a letter. Online and physical communities have a different architectural base, but the social level is still people communicating with people. This suggests computer-mediated communities operate by the same principles as physical communities; that is, virtual society is still a society, and friendships cross seamlessly from face-to-face to e-mail interaction. Table 1 suggests four computer system levels, matching the idea of an information system as hardware, software, people, and business processes (Alter, 2001). Social-technical systems arise when cognitive and social interaction is mediated by information technology rather than the natural world.