Over its short disciplinary history, computing has seen a stunning number of descriptions of the field's characteristic ways of thinking and practicing, under a large number of different labels. One of the more recent variants, notably in the context of K-12 education, is "computational thinking", which became popular in the early 2000s, and which has given rise to many competing views of the essential character of CT. This article analyzes CT from the perspective of computing's disciplinary ways of thinking and practicing, as expressed in writings of computing's pioneers. The article describes six windows into CT from a computing perspective: its intellectual origins and justification, its aims, and the central concepts, techniques, and ways of thinking in CT that arise from those different origins. The article also presents a way of analyzing CT over different dimensions, such as in terms of breadth vs. depth, specialization vs. generalization, and in terms of skill progression from beginner to expert. Those different views have different aims, theoretical references, conceptual frameworks, and origin stories, and they justify their intellectual essence in different ways. [Note: The issue number (1) shown on the PDF is incorrect. The correct citation for this article is v20 n3.]