The early phases of computer supported research in history have been characterized by enthusiasm about the many possibilities opened. Possibilities, which go beyond just one methodological paradigm as the recent discussions about the relative importance of quantitative studies within computer applications in history show. A deeper discussion about these developments is necessary, necessary for pure intellectual reasons as well as for ones within the politics of academia. This requires a theory of historical computing, which starts from an analysis of the differences between computing in history and computers' applications to other disciplines. To illustrate that, a number of examples are given, which show that the information presented by historical sources is inherently different from the one processed by information systems directed at current times.