Understanding Virtual Machines
1. A virtual machine is a software computer that, like a physical machine, runs an operating system and applications.
2. A virtual machine uses the physical resources of the physical machine on which it runs, which is called the host system.
3. Virtual machines have virtual devices that provide the same functionality as physical hardware, but with the additional benefits of portability, manageability, and security.
4. A virtual machine has an operating system and virtual resources that you manage in much the same way that you manage a physical computer.
Further part you can refer direct from VM Workstation book.
Kindly go through the link.
Type 1 Hypervisor
Type 1 (or native, bare-metal) hypervisors are
software systems that run directly on the host’s hardware to control the
hardware and to monitor guest operating-systems. A guest operating
system thus runs on another level above the hypervisor. Some examples
are VMware ESX, Xen, Microsoft Hyper-V, etc.
Type 1 hypervisors are appropriate when you want to provide the only
OS that is used on a client. When a user turns a machine on, he only
sees a single OS that looks and feels local.
Type 2 Hypervisor
Type 2 (or hosted) hypervisors are software applications running within a conventional operating-system
environment. Considering the hypervisor layer as a distinct software
layer, guest operating systems thus run at the third level above the
hardware. Some examples are VMware Workstation, VMware Fusion, MED-V, Windows Virtual PC, VirtualBox, Parallels, MokaFive, etc.
Type 2 hypervisors are appropriate when you want a user to have
access to their own local desktop OS in addition to the
centrally-managed corporate VDI OS. This could be for an employee-owned PCscenario,
or it could be a situation where you have contractors, etc., who need
access to their personal apps and data in addition to the company’s apps
and data.
Client Hypervisors
Over the past 5 years, Type 1 hypervisors are dominantly used in the
server market, whereas, Type 2 hypervisors are being used on clients,
i.e., desktops and laptops. Recently, the need for a Type 1 hypervisor
that runs locally on a client device, called the client hypervisor, has
emerged for supporting the Virtual Desktop Infrastructure VDI).
Benefits
VDI’s promise lies in realizing a significant cost reduction for
managing desktops. A client hypervisor is useful because it combines
the centralized management of VDI with the performance and flexibility
of local computing. It offers several advantages:
- It provides a Hardware Abstraction Layer so that the same virtual disk image can be used on a variety of different devices.
- The devices do not need a “base OS” when the client hypervisor is present. The maintenance overhead of patching a “base OS” frequently on each of the devices is greatly reduced.
- Once a virtual disk image has been provisioned, it runs and the display is driven locally. This frees up the client from the need to support remote display protocols.
- It decouples the management of the device from the management of Windows and the user; administrators can spend their time focusing on user needs instead of device maintenance.
Type 1 Server and Client Hypervisors
Server hypervisors are designed to make VMs portable and increasing the utilization of physical hardware. Client hypervisors are intended to increase the manageability of the client device and improve security by separating work and personal VMs.
The bottom line is that even though they’re both called “Type 1″ or “bare-metal hypervisors,” there are some philosophical differences in how each came to be. (This could help explain why it has taken over five years to extend the Type 1 hypervisor concept from the server to the desktop.)
| Dimension | Type 1 Server Hypervisor | Type 1 Client Hypervisor |
| Design Goal | Host multiple VMs and make each VM seem like a “real” server on the network. | The user shouldn’t even know that there is a hypervisor or they are using a VM. |
| Virtualization Goal | I/O: Disk and Networking | Native device support that affects user experience, e.g., a) GPU and graphics capabilities b) USB ports and devices c) Laptop battery and power state d) Suspend/Hibernate states |
| Tuning | Maximum simultaneous network, processor and disk I/O utilization | Graphics, multimedia and wireless connectivity |
| Hardware Support | Narrow set of different preapproved hardware models | Should (ideally) run on just about anything |
| Intrusiveness | Controls most if not all of the hardware platform and devices and provide a near complete emulated and/or para-virtualized device model to the virtual machines running on top | a) Should support full device pass-through to a guest VM. b) Should also support dynamic assignment and “switching” of devices between different guests |
Type 1 Client Hypervisor Vendors
In the Type 1 client hypervisor space, there are Neocleus NeoSphere and Virtual Computer NXTop. There are product announcements from both VMware and Citrix, however, there is no shipping product to date. There is also the Xen Client Initiative – an effort to port the open source Xen hypervisor to the client.
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