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       A hypervisor or virtual machine monitor (VMM) is a piece of computer software, firmware or hardware that creates and runs virtual machines.         A computer on which a hypervisor is running one or more virtual machines is defined as a host machine. Each virtual machine is called a guest machine. The hypervisor presents the guest operating systems with a virtual operating platform and manages the execution of the guest operating systems. Multiple instances of a variety of operating systems may share the virtualized hardware resources. Classification        In their 1974 article "Formal Requirements for Virtualizable Third Generation Architectures" Gerald J. Popek and Robert P. Goldberg classified two types of hypervisor: Type-1, native or bare-metal hypervisors        These hypervisors run directly on the host's hardware to control the hardware and to manage guest operating systems. For this reason, they are sometimes called bare metal hyperv

A logical partition, commonly called an LPAR, is a subset of computer's hardware resources, virtualized as a separate computer. In effect, a physical machine can be partitioned into multiple logical partitions, each hosting a separate operating system. History IBM developed the concept of hypervisors (virtual machines in CP-40 and CP-67) and in 1972 provided it for the S/370 as Virtual Machine Facility/370. IBM introduced the Start Interpretive Execution (SIE) instruction (designed specifically for the execution of virtual machines) as part of 370-XA architecture on the 3081, as well as VM/XA versions of VM to exploit it. PR/SM is a type-1 Hypervisor based on the CP component of VM/XA that runs directly on the machine level and allocates system resources across LPARs to share physical resources. It is a standard feature on IBM System z, System p, and System i machines. The terms PR/SM and LPAR are often used interchangeably, including in IBM documentation. Formally, L

          Logical Domains (LDoms or LDOM) is the server virtualization and partitioning technology for SPARC V9 processors. It was first released by Sun Microsystems in April 2007. After the Oracle acquisition of Sun in January 2010, the product has been re-branded as Oracle VM Server for SPARC from version 2.0 onwards.          Each domain is a full virtual machine with a reconfigurable subset of hardware resources. Domains can be securely live migrated between servers while running. Operating systems running inside Logical Domains can be started, stopped, and rebooted independently. A running domain can be dynamically reconfigured to add or remove CPUs, RAM, or I/O devices without requiring a reboot.

          Secure Shell, or SSH, is a cryptographic (encrypted) network protocol to allow remote login and other network services to operate securely over an unsecured network.         SSH provides a secure channel over an unsecured network in a client-server architecture, connecting an SSH client application with an SSH server. Common applications include remote command-line login and remote command execution, but any network service can be secured with SSH. The protocol specification distinguishes between two major versions, referred to as SSH-1 and SSH-2.          The most visible application of the protocol is for access to shell accounts on Unix-like operating systems, but it sees some limited use on Windows as well. In 2015, Microsoft announced that they would include native support for SSH in a future release.                SSH was designed as a replacement for Telnet and for unsecured remote shell protocols such as the Berkeley rlogin, rsh, and rexec protocols. Th

        Remote Desktop Protocol (RDP) is a proprietary protocol developed by Microsoft, which provides a user with a graphical interface to connect to another computer over a network connection. The user employs RDP client software for this purpose, while the other computer must run RDP server software.         Clients exist for most versions of Microsoft Windows (including Windows Mobile), Linux, Unix, OS X, iOS, Android, and other operating systems. RDP servers are built into Windows operating systems; an RDP server for Unix and OS X also exists. By default, the server listens on TCP port 3389 and UDP port 3389.           Microsoft currently refers to their official RDP server software as Remote Desktop Connection, formerly "Terminal Services Client".           The protocol is an extension of the ITU-T T.128 application sharing protocol.

        In computing, paravirtualization is a virtualization technique that presents a software interface to virtual machines that is similar, but not identical to that of the underlying hardware.       The intent of the modified interface is to reduce the portion of the guest's execution time spent performing operations which are substantially more difficult to run in a virtual environment compared to a non-virtualized environment. The paravirtualization provides specially defined 'hooks' to allow the guest(s) and host to request and acknowledge these tasks, which would otherwise be executed in the virtual domain (where execution performance is worse). A successful paravirtualized platform may allow the virtual machine monitor (VMM) to be simpler (by relocating execution of critical tasks from the virtual domain to the host domain), and/or reduce the overall performance degradation of machine-execution inside the virtual-guest.         Paravirtualization requires

Operating-system-level virtualization is a server-virtualization method where the kernel of an operating system allows for multiple isolated user-space instances, instead of just one. Such instances (sometimes called containers, software containers, virtualization engines (VE), virtual private servers (VPS), or jails) may look and feel like a real server from the point of view of its owners and users. On Unix-like operating systems, one can see this technology as an advanced implementation of the standard chroot mechanism. In addition to isolation mechanisms, the kernel often provides resource-management features to limit the impact of one container's activities on other containers. Uses Operating-system-level virtualization is commonly used in virtual hosting environments, where it is useful for securely allocating finite hardware resources amongst a large number of mutually-distrusting users. System administrators may also use it, to a lesser extent, for consolidati

      Linux-VServer is a virtual private server implementation that was created by adding operating system-level virtualization capabilities to the Linux kernel. It is developed and distributed as open-source software.         The project was started by Jacques Gélinas. It is now maintained by Herbert Pötzl of Austria and is not related to the Linux Virtual Server project, which implements network load balancing.        Linux-VServer is a jail mechanism in that it can be used to securely partition resources on a computer system (such as the file system, CPU time, network addresses and memory) in such a way that processes cannot mount a denial-of-service attack on anything outside their partition.         Each partition is called a security context, and the virtualized system within it is the virtual private server. A chroot-like utility for descending into security contexts is provided. Booting a virtual private server is then simply a matter of kickstarting init in a new

          A hybrid hosting service or hybrid server is a type of Internet hosting which is a combination of a physically-hosted server with virtualization technology.           A hybrid server is a new kind of dedicated server that offers both the power of a classic dedicated server and the flexibility of cloud computing. On hybrid dedicated servers hardware are 100% allocated to user. The price is lower than for dedicated servers.          The server is separated into hybrid server environments using Red Hat KVM or any other virtualization. Each hybrid environment is securely isolated and has guaranteed resources available to it which ensures a high level of performance and responsiveness. A hybrid server combines all of the benefits of virtualization technology with the performance of a full dedicated server. So, an administrator can use automation to suspend, restart, or reinstall the operating system. One large server is split into a few (normally two) Hybrid servers.