A virtual private server (VPS), also called a virtual dedicated server (VDS), is a virtual server that appears to the user as a dedicated server, but that is actually installed on a computer serving multiple websites. A single computer can have several VPSs, each one with its own operating system (OS) that runs the hosting software for a particular user.
A VPS hosting provider relies on virtualization software, called a hypervisor, to abstract resources on a physical server and provide customers with access to an emulated server, called a virtual machine (VM). Each virtual machine runs a complete operating system, and has restricted access to a portion of the physical server's compute, memory and storage resources. Customers have access to the VM's OS, but not to the physical server.
While multiple tenants can share VMs that reside on the same physical server, those VMs are restricted from interacting with VMs owned by other tenants, hence creating a server that is logically private, but not physically separate.
One of the primary advantages to using a VPS, as opposed to a traditional web hosting service, is that the subscriber has full access to the VPS's OS, with unrestricted root or administrator permissions. This level of access allows subscribers to configure the VPS to meet their own unique requirements.
The subscriber may also opt to host additional services on the server, such as a File Transfer Protocol site, a mail server, or specialized applications and dependency databases for activities such as e-commerce and blogging.
Another advantage to using a VPS is that it allows the subscriber to host multiple websites. An organization might, for instance, host its production website and a development site on the same VPS. Similarly, a web development company may lease a VPS and use it to host websites for multiple customers.
VPSs are commonly used by smaller organizations that want the flexibility of a dedicated server, but without the cost. Although a VPS can meet this requirement, it does have its disadvantages.
The primary disadvantage to using a VPS is its lack of performance. The organization that provides the VPS will typically throttle the server's performance in an effort to maximize the number of VPSs that the physical server is able to accommodate. In the unlikely event that the VPS's performance is not throttled, it then becomes possible for an adjacent VPS to consume excessive resources, to the point of impacting the VPS's performance.
Another possible disadvantage to using a VPS is security. VPSs are usually based on server virtualization, which should be able to keep VPSs adequately isolated from one another. Even so, those with significant security requirements commonly avoid multi-tenant environments as a best practice.