While commercial off-the-shelf (COTS) operating systems (OS) have long been widely used, the issue regarding their robustness is far from being solved. Although many efforts have been made in this research domain, people still find it difficult to make choices among various OSs for robustness concerns. This paper proposes a reference model for OS robustness forecast and selection that aims to forecast the robustness of specific OSs under given operational profiles. At the same time, the model can select appropriate OSs as development/operating platforms that meet the particular robustness requirements of the target workloads. Our model combines OSspsila overall robustness with operational profiles and uses extensive tests on OS APIs to make our calculation. We have measured 255 APIs and C-library functions on windows XP and Vista, and 197 C-library functions on Linux 2.6.22 (Ubuntu 7.10). Our results show that on average Windows XP and Vista are more robust than Linux, but their performances are comparable under compute-intensive workloads. A demonstration of how these results are used in the proposed reference model for OSs robustness forecast and selection is given at the end.