Introduction
- Command layer
Usually we call it the shell, which is the interface for users to interact with OS - Service layer
Contains a set of utility functions that will be used or called by application programs and the command layer - Kernel
Which is the core of OS; it manages resources and directly interacts with computer hardware
Operations systems are complex, and architectures help manage this complexity by:
- organizing system components
- defining the privileges levels where each component exectes
Examples include Monolithic, layers, microkernel, modular.
- User mode
The mode in which user programs run. Only a subset of instructions can be executed in this mode, and the CPU cannot access hardware directly. - Kernel mode
CPU is in kernel mode when OS kernel executes. Can execute any instruction.