1. Virtual Servers

2. VMM
VMM was defined as the software-abstraction layer which partitions a hardware system into multiple virtual machines.

5. Hypervisor
A hypervisor or virtual machine monitor (VMM) is a piece of computer software, firmware or hardware that creates and runs virtual machines.
Two type Hypervisor
Type 1 (or native, bare metal) hypervisors:run directly on the host's hardware to control the hardware and to manage guest operating systems.
A guest operating-system thus runs on another level above the hypervisor
Type 2 (or hosted) hypervisors:run within a conventional operating-system environment

6. Two types of Hypervisor

7. Bare Metal
This model represents the classic implementation of virtual-machine architectures;
IBM developed the original hypervisors as bare-metal tools in the 1960s: the test tool, SIMMON, and CP/CMS. CP/CMS was the ancestor of IBM's z/VM.
Modern equivalents include Oracle VM Server for SPARC, Oracle VM Server for x86, the Citrix XenServer, VMware ESX/ESXi and Microsoft Hyper-V 2008/2012.

8. Hosted Hypervisor
With the hypervisor layer as a distinct second software level, guest operating-systems run at the third level above the hardware. VMware Workstation and VirtualBox

9. Thee Virtualization Approaches
Full Virtualization
Paravirtualization
Hardware-assisted Virtualization

10. Full Virtualization

11. Full Virtualization (cont)
guest operating system is not aware that it is residing as a virtual machine on a physical host, therefore no modifications will be made on the OS kernel.
since all the interactions of the virtual machine and the physical hardware are being managed by the VMM or the Hypervisor, the VMM will require their own processing needs.
This means that the physical system must reserve some of its resources for the hypervisor to operate.
An example of full virtualization systems would be Vmware ESX and the Microsoft Hyper-V

12. Paravirtualized

13. Paravirtualization
guest operating systems are aware that they are residing on virtual machines and that they are sharing resources with other VMs.
The VMM in this model does not need a lot of processing power in order to manage the VMs residing on the physical system.
This is due to the fact that each OS on a VM is aware of the needs of the other OS for resources on the physical system.
Paravirtualization modifies the kernel of the OS in order to replace instructions which were not virtualized since, in this method, the hardware is partially simulated.
The replaced instructions in this process are referred to as “hypercalls” which assist in the communication between host operations and the OS of the virtual machine
. Examples: XenServer and IBM z/VM.

14. Hardware assisted virtualization
hardware-assisted virtualization is a platform virtualization approach that enables efficient full virtualization using help from hardware capabilities, primarily from the host processors.
Full virtualization is used to simulate a complete hardware environment, or virtual machine, in which an unmodified guest operating system (using the same instruction set as the host machine) executes in complete isolation.
Hardware-assisted virtualization was added to x86 processors (Intel VT-x or AMD-V) in 2006.
Hardware-assisted virtualization is also known as accelerated virtualization; 
Xen calls it hardware virtual machine (HVM), andVirtual Iron calls it native virtualization.

15. Reduce costs by consolidating services onto the fewest number of physical machines

16. VPS
A virtual private server (VPS) is a virtual machine sold as a service by an Internet hosting service.[1]
A VPS runs its own copy of an operating system, and customers have superuser-level access to that operating system instance, so can install almost any software that runs on that OS.
For many purposes they are functionally equivalent to a dedicated physical server, and being software defined are able to be much more easily created and configured.

17. Non-virtualized Data Centers
Too many servers for too little work
High costs and infrastructure needs
Maintenance
Networking
Floor space
Cooling
Power
Disaster Recovery

18. Dynamic Data Center
Virtualization helps us break the “one service per server” model
Consolidate many services into a fewer number of machines when workload is low, reducing costs
Conversely, as demand for a particular service increases, we can shift more virtual machines to run that service
We can build a data center with fewer total resources, since resources are used as needed instead of being dedicated to single services
Or sitting and waiting until the next spike in demand