VPS Server Section

VPS Servers
it is time to explain some differend between some differend vps software for windows and linux
 first of all , you got differend virtualitation software that is used to make vps servers
so you got like virtuozo and like xen and openvz
 here are the explanations of what each do and what makes them special

Xen

Xen Source
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Paravirtualization, requiring porting of guest systems

On most CPUs, Xen uses a form of virtualization known as paravirtualization, meaning that the guest operating system must be modified to use a special hypercall ABI instead of certain architectural features. Through paravirtualization, Xen can achieve high performance even on its host architecture (x86) which is notoriously uncooperative with traditional virtualization techniques.
On x86, the Xen host kernel code runs in Ring 0, while the hosted domains run in Ring 1 or Ring 3.

Hardware assisted virtualization, allowing for unmodified guests

Both Intel and AMD have contributed modifications to Xen to support their AMD-V and Intel VT architecture extensions.These technologies, while differing quite substantially in their implementation and instruction sets, are managed by a common abstraction layer in Xen and enable unmodified guest operating systems to run within Xen virtual machines, starting with Xen 3.0.
This has been a significant development because it allows proprietary operating systems (such as Microsoft Windows) to be virtualized since the guest systems kernel does not require modification when the host runs on Intel VT or AMD-V hardware.
Hardware assisted virtualization offers new instructions to support direct calls by a paravirtualized guest/driver into the hypervisor, typically used for I/O or other so-called hypercalls. It also provides additional execution modes: "root mode" and "non-root mode". Both of these modes have Rings 0-3; the Xen host operates in root mode and has access to the real hardware, while the unmodified guest operates in Rings 0-3 of non-root mode and its "hardware" accesses are under complete control of the hypervisor.
Xen-HVM has device emulation based on the QEMU project to provide I/O virtualization to the VMs. Hardware is emulated via a patched QEMU "device manager" (qemu-dm) daemon running as a backend in dom0. This means that the virtualized machines see as hardware: a PIIX3 IDE (with some rudimentary PIIX4 capabilities), Cirrus Logic or vanilla VGA emulated video, RTL8139 or NE2000 network emulation, PAE, and somewhat limited ACPI and APIC support and no SCSI emulation.
As of Xen 3.0.2, the list of supported unmodified guests is limited to certain versions of Windows (incl. XP) and Linux.

parallells / virtuozo

Parallels Logo
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Functionalities

Parallels Workstation is a hardware emulation virtualization software, in which a virtual machine engine enables each virtual machine to work with its own processor, RAM, floppy drive, CD drive,I/O devices, and hard disk – everything a physical computer contains. Parallels Workstation virtualizes all devices within the virtual environment, including the video adapter, network adapter, and hard disk adapters. It also provides pass-through drivers for parallel port and USB devices.
Because all guest virtual machines use the same hardware drivers irrespective of the actual hardware on the host computer, virtual machine instances are highly portable between computers. For example, a running virtual machine can be stopped, copied to another physical computer, and restarted.
Parallels Workstation is able to virtualize a full set of standard PC hardware, including:
  • A Pentium or AMD Duron processor
  • A generic motherboard compatible with Intel i815 chipset
  • Up to 1.5GB of RAM (even though the real i815 only supports 512 MB)
  • VGA and SVGA video cards with VESA 3.0 support
  • A 1.44 MB floppy drive, which can be mapped to a physical drive or to an image file.
  • Up to four IDE devices. This includes virtual hard drives that range in size from 20 MB to 128 GB each and CD/DVD-ROM drives. IDE devices can be mapped to physical drive or to an image file.
  • Up to four serial ports that can be mapped to a real port, to a pipe or to an output file.
  • Up to three bi-directional parallel ports, each of which can be mapped to a real port, to a real printer or to an output file.
  • An Ethernet virtual network card compatible with Realtek RTL8029(AS).
  • 2-port USB 1.1 controller.
  • An AC97 compatible sound card.
  • A 104-key Windows enhanced keyboard and a PS/2 wheel mouse.

    • Known issues

    Known limitations of Parallels Workstation, as of August 2009, include the following:
  • Can only run 32-bit operating systems.
  • Inability to assign multiple CPUs to your virtual machine to gain additional performance for CPU-intensive workloads.
  • DVD/CD-ROM "pass-through" access has not been implemented, which means that it is impossible to use DVD and CD burners exclusively in guest virtual machines.
  • Supported memory limit for all virtual machines is 4 GB, and memory limit for a single virtual machine is 1500 MB.
  • Devices such as USB mice, memory keys, webcams, and mobile phones have been cited on the company's support forum as not working correctly[citation needed].
  • Network emulation does not support NAT


    • OpenVZ

    OpenVZ Virtualisation
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    OpenVZ compared to other Virtualization Technologies

    OpenVZ is not true virtualization but really containerization like BSD Jails. Technologies like VMWare and XEN are more flexible in that they virtualize the entire machine and can run multiple operating systems. OpenVZ uses a single patched Linux kernel and therefore can run only Linux. However because it doesn't have the overhead of a true hypervisor it is very fast and efficient. The obvious big disadvantage is the single kernel. All virtual servers have to be happy with the Linux kernel version that the host runs on.
    The advantages however are that memory allocation is soft in that memory not used in one virtual environment can be used by others or for disk caching. So if a gig of ram is allocated but not used then it is available to others. OpenVZ uses a common file system so each virtual environment is just a directory of files that is isolated using chroot. Thus a virtual machine can be cloned by just copying the files in one directory to another and creating a config file for the virtual machine and starting it.