A virtual private server (VPS) is a virtual machine sold as a service by an Internet hosting service.
VPS runs its own copy of an operating system, and customers have superuser-level
access to that operating system instance, so they can install almost any
software that runs on that OS. For many purposes they are functionally
equivalent to a dedicated physical server, and being software-defined, are able
to be much more easily created and configured. They are priced much lower than
an equivalent physical server, but as they share the underlying physical
hardware with other VPSs, performance may be lower, and may depend on the
workload of other instances on the same hardware node.
The force driving
server 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
Partitioning a single server to appear as multiple servers has
been increasingly common on microcomputers since the launch of VMware ESX Server
in 2001. The physical server typically runs a hypervisor which is tasked with
creating, releasing, and managing the resources of "guest" operating systems, or
virtual machines. 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 save 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, RAM, and disk space.
Although VMware and Hyper-V dominate
in-house corporate virtualization, they are less common for VPS providers,
mainly due to cost and limitations - who typically use products such as OpenVZ,
Virtuozzo, Xen or KVM.
Many companies offer virtual private server
hosting or virtual dedicated server hosting as an extension for web hosting
services. There are several challenges to consider when licensing proprietary
software in multi-tenant virtual environments.
With unmanaged or
self-managed hosting, the customer is left to administer his own server
Unmetered hosting is generally offered with no limit on the
amount of data-transferred on a fixed bandwidth line. Usually, unmetered
hosting is offered with 10 Mbit/s, 100 Mbit/s or 1000 Mbit/s (with some as
high as 10Gbit/s). This means that the customer is theoretically able to use
3.33~ TB on 10 Mbit/s, 33~ TB on 100 Mbit/s and 333~ TB on a 1000 Mbit/s line
per month (although in practice the values will be significantly less). In a
virtual private server, this will be shared bandwidth and (should) mean there is
a fair usage policy involved. Unlimited hosting is also commonly marketed but
generally limited by acceptable usage policies and terms of service. Offers of
unlimited disk space and bandwidth are always false due to cost, carrier
capacities and technological boundaries.