Virtual private servers or Virtual dedicated servers are a form of virtualization that split a single physical server into multiple virtual servers. The practice of partitioning a single server so that it appears as multiple servers has long been common practice in mainframe computers, but has seen a resurgence lately with the development of software and technologies such as VMware, Xen, FreeBSD Jail, User-mode Linux, Linux-VServer, FreeVPS, OpenVZ, and Virtuozzo.
Virtual private servers have also become popular for their ability to establish sandboxes. For example, a single physical server might have two virtual private servers running: one hosting the production-level (live) website, and a second which houses a copy of it. When updates to crucial parts of software need to be made, they can be tested in the second VPS, allowing for detailed testing to be conducted without requiring several physical servers.Virtual private servers bridge the gap between shared web hosting services and dedicated hosting services, giving independence from other customers of the VPS service in software terms but at less cost than a physical dedicated server. As a VPS runs its own copy of its operating system, customers have superuser-level access to the machine, and can install almost any software that runs on the OS. Certain software does not run well in a virtualized environment, including firewalls, anti-virus clients, and indeed virtualizers themselves; some VPS providers place further restrictions, but they are generally lax compared to those in shared hosting environments. Due to the number of virtualization clients typically run on a single machine, a VPS generally has limited processor time, RAM, and disk space.
Virtual private servers are also sometimes employed to provide honeypots, allowing a machine to deliberately run software with known security flaws. Because it is possible to quickly deploy multiple virtual private servers on a single computer, honeypots are much easier to deploy, allowing better insight into the world of computer security.