Table of Contents


Operating System (OS) - the layer of software with the application programs and users above it and the machine below it


Operating systems are: Examples of operating systems are:

Overall View of Operating System:

Making a Request to the OS
       |	request (sent as a trap after a system call)
|                     NUCLEUS			       |
       |	request (sent as an interrupt)

Two crucial terms:

Major Services Provided by an Operating System:
1. process management and scheduling
2. main-memory management
3. secondary-memory management
4. input/output system management, including interrupt handling
5. file management
6. protection and security
7. networking
8. command interpretation

Other Services Provided by Operating Systems:
1. error detection and handling
2. resource allocation
3. accounting
4. configuration

Other Goals of OS Design:
1. easy to extend
2. portable - easy to move to different hardware
3. easy to install
4. easy to uninstall

The nucleus deals with the following:

  1. Interrupt/trap handling
    - OS contains interrupt service routines (interrupt handlers), typically one for each possible type of interrupt from the hardware
    - Example: clock handler: handles the clock device, which ticks 60 (or more) times per second
    - OS also contains trap service routines (trap handlers), typically one for each possible type of trap from the processor
  2. Short term scheduling - choosing which process to run next
  3. Process management - creating and deleting processes
    - assigning privileges and resources to processes
  4. Interprocess communication (ipc) - exchanging information between processes

Command Interpreter or Shell

Layered Design

Virtual Machine

Dual-Mode Operation

Other Key Concepts

Types of System Calls (Silberschatz et al., p. 66):

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