Editing Virtual private server (section)

== Virtualization ==
The force driving server [[Hardware virtualization|virtualization]] is similar to that which led to the development of [[time-sharing]] and [[multiprogramming]] in the past. Although the resources are still shared, as under the time-sharing model, virtualization provides a higher level of security, dependent on the type of virtualization used, as the individual virtual servers are mostly isolated from each other and may run their own full-fledged [[operating system]] which can be independently rebooted as a virtual instance.

Partitioning a single server to appear as multiple servers has been increasingly common on [[microcomputer]]s since the release of [[VMware ESX Server]] in 2001.<ref>{{cite journal |last=Waldspurger |first=Carl A. |title=Memory Resource Management in VMware ESX Server |journal=Proceedings of the 5th Symposium on Operating Systems Design and Implementation (OSDI '02) |date=December 2002 |location=Boston, MA |publisher=USENIX Association |pages=181–194 |url=https://www.usenix.org/conference/osdi-02/memory-resource-management-vmware-esx-server}}</ref>  VMware later replaced ESX Server with VMware ESXi, a more lightweight hypervisor architecture that eliminated the Linux-based Console Operating System (COS) used in the original ESX.<ref>{{cite web |title=VMware ESXi is a bare-metal hypervisor that installs directly onto your physical server |url=https://endoflife.date/vmware-esxi |website=endoflife.date |access-date=May 12, 2025}} </ref> 
The physical server typically runs a [[hypervisor]] which is tasked with creating, releasing, and managing the resources of "guest" operating systems, or [[virtual machine]]s. These guest operating systems are allocated a share of resources of the physical server, typically in a manner in which the guest is not aware of any other physical resources except for those allocated to it by the hypervisor. As a VPS runs its own copy of its operating system, customers have [[superuser]]-level access to that operating system instance, and can install almost any software that runs on the OS; however, due to the number of virtualization clients typically running on a single machine, a VPS generally has limited processor time, [[random access memory|RAM]], and disk space.<ref>{{cite web|url=https://www.online-sciences.com/computer/vps-web-hosting-virtual-private-server-advantages-and-disadvantages/ |title=VPS Web Hosting ( Virtual Private Server ) advantages and disadvantages|work=online-sciences.com |date=18 December 2015 |access-date=13 February 2019}}</ref>

There are several approaches to virtualization. In [[Virtualization#Hardware_virtualization|hardware virtualization]], a [[hypervisor]] such as the [[Kernel-based Virtual Machine]] allows each virtual machine (VM) to run its own independent kernel, providing greater isolation from the host system. By contrast, [[Containerization (computing)|container-based virtualization]]—for example [[OpenVZ]]—shares the host kernel among multiple containers. This can improve resource efficiency, but usually offers less isolation and fewer customization options for each instance.<ref name="KVMvsOpenVZ">{{cite web |title=What is a KVM VPS? |url=https://www.liquidweb.com/vps/what-is-kvm-vps/ |website=Liquid Web |access-date=12 May 2025}}</ref>