Virtual Machine (VM)
A virtual machine is a (generally heavier) which runs on the host operating system – OS. This software allows to launch one or more guest OS. The virtual machine and / or emulates the hardware for the guest OS, they believe that interact directly with hardware.
This solution is very similar to an emulator, and sometimes can be easily confused as one. However, the unit of computation, i.e., the microprocessor, the working memory (RAM), and memory storage (via a file) are directly accessible to virtual machines, while an emulator on the unit is simulated, and the performance is considerably reduced compared to true virtualization.
This solution separates good OS guests, but it carries a cost in performance. This cost can be very high if the processor must be emulated, as is the case in the emulation. In return, this solution allows combining several heterogeneous OS on a single web server with complete isolation. The exchange between the virtual private servers are made via the standard channels of communication between operating systems (TCP / IP and other network protocols), and a buffer exchange can emulate virtual network cards on a single network card.
* QEMU: emulator platforms x86, PPC, Sparc
* KVM: modified version of QEMU drawing instructions virtualization AMD and Intel processors (Intel VT or AMD-V)
* Bochs: x86 emulator
* Guest PC Lismoresystems owner, emulator x86 on PC hardware
* MacOnLinux: emulator platform Mac OS on Linux PPC
* Microsoft and Microsoft VirtualPC VirtualServer owner, x86 emulator
* Parallels: owner
* PearPC: PPC emulator platform on x86 hardware
* Plex86: x86 emulator
* VirtualBox: x86 emulator
* VMware: owner emulator x86 (products VMware Server, VMware Player and VMware Workstation)
* Hercules: emulator that allows the emulation of a mainframe z / OS on a PC with Windows or Linux disk emulation
Para Virtualization Or Hypervisor
A hypervisor is a very lightweight kernel and optimized to manage the access of guest OS kernel to the hardware architecture underlying. If the OS work with guests are to be aware virtualized, and are optimized for this, known as para-virtualization (Method essential Hyper-V Microsoft and increases performance on VMware ESX for example).
Currently the method Hypervisor virtualization infrastructure is considered more efficient, but it has the disadvantage of being expensive and binding, while allowing more flexibility in the case of a virtual data center.
Several solutions are on the market, it is interesting to make a small thumbnail. Xen is a Hypervisor originally developed by the University of Cambridge in the UK and now owned by Citrix, it uses a lightweight kernel that supports the Linux kernel, Plan9, NetBSD, etc.. VMware is a mature product, ESX, which is part of a global offer to virtualize computer resources of the company. Microsoft has released a Hypervisor based on the same principles as its competitors. The Hypervisor from Microsoft is included in Windows Server 2008 (64bit version only).
* VMware: owner, x86 Hypervisor (ESX and ESXi products-Free-)
* Xen: lightweight kernel supports kernel Linux, Plan9, NetBSD, etc..
* Hyper-V: owner (Microsoft), hypervisor for x86.
* Proxmox: Free (based on Debian) under GNU / GPL license, virtual machine hypervisor
Support for virtualization can be integrated with the processor or assisted by one, loading equipment, for example, to virtualize memory access or to protect the physical processor accesses the lowest level. This allows to simplify the virtualization software and reduce the degradation of performance and offer it as a Cheap VPS Hosting solution to users.
Examples of hardware virtualization:
* Hypervisor IBM Power & Micro-partitioning, AIX
* Mainframe: VM / CMS
* Sun LDOMs (hypervisor to manage “logical domains”)
* Sun E10k/E15k
* HP Superdome
* AMD-V (Support AMD Virtualization, formerly Pacifica)
* Intel VT (Virtualization Support for Intel, formerly Vanderpool)
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