There are many things in OSTEP that I found really eye opening. One thing that stuck with me was that at some point, when discussing virtualization, it referred

There are many things in OSTEP that I found really eye opening. One thing that stuck with me was that at some point, when discussing virtualization, it referred to an OS as a virtual machine, and that really changed the way I look at operating systems now. > That is, the OS takes a physical resource (such as the processor, or memory, or a disk) and transforms it into a more general, powerful, and easy-to-use virtual form of itself. Thus, we sometimes refer to the operating system as a virtual machine.