Modern Operation System

This is the reading note to the book MODERN OPERATING SYSTEMS 4th, written by Andrew S. Tanenbaum, Herbert Bos

Introduction

Operating system is a layer of software whose job is to provide a unified model of the computer and to handle managing all the resources
Appearances can be deceiving:
- User interact shell when the program is text based
- And GUI(Graphical User Interface) when the program uses icons.
Overview:
- $ \overbrace {Physical}^{Hardware}\ |\ \overbrace{\underbrace{Operating\ system}{Kernel\ Mode}\ |\ \underbrace{User\ Interface\ Program\ |\ Apps}{User\ Mode}}^{Software} $
- Kernel mode(also called supervisor mode) has complete access to all the hardware.
- User mode usually gets denied to affect the control of the machine or do I/O operations. Only a sbuset of machine instructions is available
- The user interface program, shell or GUI, is the lowest level of user-mode software. Multiple apps can be launched from it, such as a web broswer, etc.
- The Operating System runs on the bare hardware and provides the base for all the other software.