Operating Systems Introduction

The Von Neumann Model

The OS

virtualization - 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

Virtualization

• Virtualizing The CPU
• Virtualizing Memory

Concurrency

• Multiple processes
• Multiple threads within a process

Persistence

• Saving data to disk
• The filesystem
  • Files
  • Directories

Design Goals

• Provide a set of abstractions in order to make the system convenient and easy to use.
• Provide high performance
• Minimize overheads
• Protection and security
• Energy efficiency

Some History

• Early Operating Systems: Just Libraries
• Beyond Libraries: Protection
• The Era of Multiprogramming

The Modern Era

Hardware support and protection and well-defined boundaries.

Kernel Space

• All machine instructions are available.
• All memory addresses are available.

User Space

• A subset of the instructions are available. Typically I/O instructions and instructions that change the mode bit are not available. Using those instructions causes the process to fault and stop.
• A subset of the memory addresses are available.