Abstract
The FreeBSD, GNU/Linux, Solaris, and Windows operating systems have kernels that provide comparable facilities. Interestingly, their code bases share almost no common parts, while their development processes vary dramatically. We analyze the source code of the four systems by collecting metrics in the areas of file organization, code structure, code style, the use of the C preprocessor, and data organization. The aggregate results indicate that across various areas and many different metrics, four systems developed using wildly different processes score comparably. This allows us to posit that the structure and internal quality attributes of a working, non-trivial software artifact will represent first and foremost the engineering requirements of its construction, with the influence of process being marginal, if any.

This last limitation means that the study fails to take into account the large and important set of quality attributes that are typically determined at runtime: functionality, reliability, usability, and efficiency. However, these missing attributes are affected by configuration, tuning, and workload selection. Studying them would introduce additional subjective criteria. The controversy surrounding studies comparing competing operating systems in areas like security or performance demonstrates the difficulty of such approaches.