Types of Hypervisor Technology Part-I

Depending on their implementation, there are basically two types of ways in which Hypervisors work. They are called Type I and Type II hypervisors. All products that implement Hypervisor technology fall into one of these two types.

Type I Hypervisors.

Type I Hypervisors run directly on the Hardware. Instead of the Operating system, they are fully in charge of the management of system resources. The operating systems run on top of the Hypervisor which intercepts their requests and manages them in such a way that they are completely independent of each other Figure

A Type I approach to Hypervisors

As can be seen in Figure 1, the three guest operating systems (OS’s) are running on top of the hypervisor. The OS’s see only those resources that the Hypervisor presents to them. As can be seen from the above figure, the guest operating systems run at the second level above the hardware. 

Part-II http://world-of-virtualization.blogspot.com/2009/01/types-of-hypervisor-technology-part-ii.html

Hyper-V : Introduction

Server virtualization, also known as hardware virtualization, is a hot topic in the IT world because of the potential for serious economic benefits. Server virtualization enables multiple operating systems to run on a single physical machine as virtual machines (VMs). With server virtualization, you can consolidate workloads across multiple underutilized server machines onto a smaller number of machines. Fewer physical machines can lead to reduced costs through lower hardware, energy, and management overhead, plus the creation of a more dynamic IT infrastructure.

Hyper-V, the next-generation hypervisor-based server virtualization technology, as a role, plus flexible licensing policies, it's now easier than ever to take advantage of the cost savings of virtualization through Windows Server 2008. This enables you to make the best use of your server hardware investments by consolidating multiple server roles as separate virtual machines (VMs) running on a single physical machine and also efficiently run multiple different operating systems—Windows, Linux, and others—in parallel, on a single server, and fully leverage the power of x64 computing.

The hypervisor is a layer of software that runs above the physical hardware and below one or more operating systems. The hypervisor's main purpose is to provide isolated execution environments called partitions. The hypervisor provides each partition with the partition's own set of hardware resources (for example, memory, devices, and CPU cycles). The hypervisor must control and arbitrate access to the underlying hardware.

The Windows hypervisor, part of Hyper-V, performs the following tasks:

• Creates logical partitions.
• Manages memory and processor scheduling for guest OSs.
• Provides mechanisms in order to virtualizes input/output and communicate among partitions.
• Enforces memory access rules.
• Enforces policy for CPU usage.
• Exposes a simple programmatic interface known as hypercalls.

Types Of Virtualization

• Server Hardware Virtualization. Server Hardware Virtualization runs a very lightweight core operating system. The hypervisor can host independent virtual machines (VMs). This form of virtualization requires hardware that has embedded virtualization awareness capabilities. Since the hypervisor is very lightweight, there is little overhead in the system, which allows for more scalability in the virtual machines.
  
  
• Server Software Virtualization. An operating system, such as Windows Server® 2003 or Windows Server 2008, runs an application that is able to host virtual machines. Each virtual machine runs a completely separate operating system and application set.
  
  
• Presentation Virtualization. Centralized systems host multiple user sessions, and all processing is done on those host systems. The user sessions are isolated from each other. Only the presentation information, such as keyboard and mouse inputs, and video updates are sent between the client and the host system. The client can be a full Windows-based workstation or a Windows-based terminal device.
  
  
• Application Virtualization. An application is isolated from the underlying operating system by means of wrapper software that encapsulates it. This allows multiple applications that may have conflicting dynamic link libraries (DLLs) or other incompatibilities to run on the same machine without affecting each other.
  
  
• Desktop Virtualization. This is similar to Server Software Virtualization, but it runs on client systems such as Windows Vista®. The client operating system runs a virtualization application that hosts virtual machines. This is often used when a specific person needs to run one or a limited number of legacy applications on a legacy operating system.
  

Benefits of Virtualization

1. Low Costs: can be used to consolidate the workloads of several under-utilized servers to fewer machines, perhaps a single machine (server consolidation). Related benefits (perceived or real, but often cited by vendors) are savings on hardware, environmental costs, management, and administration of the server infrastructure.
   
   
2. System Mobility: Virtualized System OR VM’s can be moved potentially from Hardware to another depending upon the availability or VM requirements.
   
   
3. Multiple OS: Virtualization is to run multiple operating systems simultaneously: different versions, or even entirely different systems, which can be on hot standby. Some such systems may be hard or impossible to run on newer real hardware.
   
   
4. Increase Availability: Server virtualization also makes restoring failed systems easier. VMs are stored as files, and so restoring a failed system can be as simple as copying its file onto a new machine. This increases the uptime of the VM.

Introduction to Virtualization

Virtualization lets one computer do the job of multiple computers, by sharing the resources of a single computer across multiple environments. Virtual servers and virtual desktops let you host multiple operating systems and multiple applications locally and in remote locations, freeing you from physical and geographical limitations. In addition to energy savings and lower capital expenses due to more efficient use of your hardware resources, you get high availability of resources, better desktop management, increased security, and improved disaster recovery processes when you build a virtual infrastructure.

Following are some definitions for Virtualization

• “Server virtualization in general terms lets you take a single physical device and install (and run simultaneously) two or more OS environments that are potentially different and have different identities, application stacks, and so on.”
  
  

• “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.”
  
  

• “Virtualization is a framework or methodology of dividing the resources of a computer into multiple execution environments, by applying one or more concepts or technologies such as hardware and software partitioning, time-sharing, partial or complete machine simulation, emulation, quality of service, and many others”.