1. Operating-System Structures

2. Operating System Structure
Monolithic
Layered
Microkernel

3. Monolithic Systems The system is a collection of procedure
Each procedure can call any other procedure
No information hiding (as opposed to modules, packages, classes)

4. Monolithic Operating System
A. Frank - P. Weisberg

5. Layered Operating System

6. Layered Approach
Advantages : modularity, Simplifies debugging and system verification
Difficulty: Careful definition of layers since a layer can use only those layers below it.
Disadvantages: Less efficient (Each layer adds overhead)

7. Microkernel System Structure
Move as much functionality as possible from the kernel into “user” space.
Only a few essential functions in the kernel:
primitive memory management (address space)
I/O and interrupt management
Inter-Process Communication (IPC)
basic scheduling
Other OS services are provided by processes running in user mode (vertical servers):
device drivers, file system, virtual memory…

8. Microkernel System Structure
Monolithic

9. Microkernel System Structure
Communication takes place between user modules using message passing.
More flexibility, extensibility, portability and reliability.
But performance overhead caused by replacing service calls with message exchanges between processes.
A. Frank - P. Weisberg

10. Microkernel Operating System
A. Frank - P. Weisberg

11. Traditional App/Server
Single OS image per machine
Software and hardware  tightly coupled
Running multiple applications  on same machine
Underutilized resources
Inflexible and costly infrastructure

12. Virtualization - Green Focus
The Reality:
Most servers only use 5-15% of their capabilities on average, while consuming 60-90% of their peak power.
The Solution - Virtualization: 
Use one server to host multiple applications.
Reduce energy consumption
Reduce CO2 emissions
Running fewer, highly utilized servers frees up space and power. Less space and power is better for environment and saves money.
Tie this back to the traditional model and use as basis for virtual model.
When you have "this" - these are the trouble areas. In order to resolve these trouble areas, move to a virtual model.
Every server virtualized saves 7000kWh of electricity annually, or about $700 in energy costs.
4 tons of CO2 are eliminated for every server virtualized, the equivalent to taking 1.5 cars off the h

13. Virtual Server Model
Hardware-independence of  operating system and applications
Virtual machines can be provisioned  to any system
Can manage OS and application  as a single unit by encapsulating  them into virtual machines

14. Virtualization
Virtualization is the creation of a virtual (rather than actual) version of something, such as an operating system, a server, a storage device or network resources.

15. Virtual Machines
Fundamental idea – abstract hardware of a single computer into several different execution environments
Several components
Host – underlying hardware system
Virtual machine manager (VMM) or hypervisor – creates and runs virtual machines by providing interface that is identical to the host
Guest – Usually an operating system
Single physical machine can run multiple operating systems concurrently, each in its own virtual machine

16. on Bare Machine Implementation VM
Non-virtual Machine
Virtual Machine
A. Frank - P. Weisberg 16

17. VM Implementation on Host OS
A. Frank - P. Weisberg

18. Virtualization – Why? Server Consolidation Disaster Recovery
Often many servers support 1 major application
Strong isolation between VMs
Virtualization saves on hardware & energy
Disaster Recovery
High Availability
Testing and Deployment
Support for legacy applications

19. Types of Virtualization
Emulation
VM emulates/simulates complete hardware
Unmodified guest OS for a different PC can be run
Bochs, VirtualPC for Mac, QEMU
Full/native Virtualization
VM simulates “enough” hardware to allow an unmodified guest OS to be run in isolation
IBM VM family, VMWare Workstation, Parallels,…

20. Types of Virtualization
Para-virtualization
VM does not simulate hardware
Use special API that a modified guest OS must use
Hypercalls trapped by the Hypervisor and serviced
Xen, VMWare ESX Server
OS-level virtualization
Allows multiple copies of a single operating system to run simultaneously.
Examples: BSD jails,Linux Vserver
Application level virtualization
provides a virtual environment for only a single application within an OS
Eg. JVM gives each java application its own set of resources and prevents conflicts between them.

21. Implementation Type 1 Hypervisor Type 2 Hypervisor Paravirtualization
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22. 4/26/2017
Type 1 Hypervisors
Figure When the operating system in a virtual machine executes a kernel-only instruction, it traps to the hypervisor if virtualization technology is present.
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Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
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23. Virtualization Platform
Type 2 Hypervisor
Applications
Applications
Applications
OS 1
OS 2
OS 3
Virtualization Platform
Applications
Base Operating System
Hardware
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25. Para-virtualization
Presents guest with system similar but not identical to hardware
Guest must be modified to run on paravirtualized hardware

26. Paravirtualization (1)
4/26/2017
Paravirtualization (1)
Figure A hypervisor supporting both true virtualization and paravirtualization.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cotter