This chapter will introduce you to the legacy processor modes, which are no longer used, and to their mostly legacy features, which are still relevant today. You will see how processors evolved and learn the details of protection rings implementation (privileged and user mode). You will also understand the meaning of Global Descriptor Table. While this information helps you understanding the architecture better, it is not crucial for assembly programming in user space.
As processors evolved, each new mode increased the machine word’s length and added new features. A processor can function in one of the following ...
