Table of Contents

Types of Operating Systems

• Personal Computers
• Mobile Devices
• Servers: Designed for use by remote human users, or programs running on remote devices.
• Embedded Hardware Designed for use by embedded devices like medical equipment.

Operating System Features

• Von Neumann architecture for computer programs
  • Instructions for the computer, called opcodes
  • Data. Can be stored, processed, and manipulated
• Multiprogramming, allowing multiple programs to be used at once
  • The OS switched the processor between different programs, allowing multiple programs to be held at once.
• Supervisor mode (Kernel) and User mode for extra protection.
  • Computer can only operate in one mode at a time. Switches between modes
  • User mode has limited privileges.
    • It can not directly access machine hardware.
    • It can’t switch to supervisor mode
  • Kernel = system/hardware code, unlimited privileges
    • Can access machine hardware
    • Can switch between modes.
• Memory Management Units (MMU)
  • Hardware devices that splits physical random-access memory (RAM) of the machine into assigned address spaces
  • Programs fail if they try to access memory outside of their assigned address spaces

Services Provided By the Kernel (Supervisor Mode)

• Bootstrap (Initialization): Bringing the machine from initial power up state into a normal functioning state
• Device Drivers: Working with hardware-level devices, and isolating the user from those details.
• Storage/Filesystems: Managing bulk storage devices (disks, flash drives, etc.). Organizing storage into directories, files, etc.
• Memory Management: Controlling and allocating physical memory, using virtual memory.
• Scheduling: Controlling virtual processors and currently running processes. Allocating processor resources.
• Security: Determining and enforcing the identity and privileges of different users and programs (User-Mode vs Kernel Mode)