Computer systems software and hardware architec- tures have become increasingly complex today. Meanwhile, cyber- attacks are becoming more and more sophisticated and target any software or hardware components of these systems. Several isolation mechanisms, at the software and the hardware layers, are now available to provide the best protection against these widespread attacks. This paper is aimed at reviewing especially hardware segregation mechanisms available in today’s CPU in order to provide better insights about the intended scope of the protection and the different threats that could be addressed by such mechanisms. An abstraction model presenting the main components of current architectures and their interactions through different communication channels is proposed to support such analysis. The study focuses on Intel and ARM architectures, and outlines various hardware isolation resources that provide a security layer to the software running on these architectures. A comparative analysis of these architectures is also presented together with a discussion of open issues and future challenges.