Before we can start discussing specific operating systems, we'll need an organizing framework for the ways that operating-system design can affect programming style for good or ill.

Overall, the design and programming styles associated with different operating systems seem to derive from three different sources: (a) the intentions of the operating-system designers, (b) uniformities forced on designs by costs and limitations in the programming environment, and (c) random cultural drift, early practices becoming traditional simply because they were there first.

Even if we take it as given that there is some random cultural drift in every operating-system community, considering the intentions of the designers and the costs and limitations of the results does reveal some interesting patterns that can help us understand the Unix style better by contrast. We can make the patterns explicit by analyzing some of the most important ways that operating systems differ.