Virtual Web Hosting (VPS Servers): A Virtual Private Server also called as Virtual Dedicated Server provides a feature of multiple virtual servers on a single server. It divides the physical server into multiple layer or servers so that each server has its own capability of running its own machine. As we divide the single physical server into many servers virtually that's why it is called as Virtual Private Server. Each virtual server can run its own operating system and can be reboot independently. Each virtual dedicated server has its own disk space, bandwidth, CPU allocation and memory. In the virtual web hosting hardware is controlled by the web host and the software and operating system is controlled by the web site owner.
Earlier the partitioning of single server into multiple servers has been done only in Mainframe computers but now days the partitioning also plays an important role in the development of virtualization software and technologies and other architectures. In simple words Virtual Private Servers are just like building which has many apartments. Each apartment has same feature but it is occupied by different persons just like that Virtual Private Server is divided into different servers with same resources but used by different web sites. In virtual web hosting each server is allocated with defined resources which only that server can use e.g. the physical server have its total RAM of 10GB and there are 50 websites hosted by the physical server so each server can get approximately 200MB RAM as its resources. It totally depends upon the number of web sites hosted by the server. Each VPS run independently from each other and each one has its own file system so no other VPS can interfere into their system. So VPS can be treated as Dedicated Server.
In a virtual private hosting firstly the main or physical server boots normally then it runs a program which boots each virtual server within a virtualization environment. The virtual server has no direct access to the hardware of the server and these servers are mainly booted through the disk image. There are 2 kinds of virtualization environments: software based and hardware based. In a software based virtualization environment, the virtual machines share the same kernel (kernel is central module of operating system. It is the part of the operating system that loads first, and it remains in main memory) and actually require the main node's resources. This type of virtualization normally has many benefits in a web hosting environment because of quota incrementing and decrementing in real time with no need to restart the node.e.g. Virtuozzo , HyperVM
In hardware virtualization environment, it partitions the real hardware resources and no burst and/or realtime quota modification is possible. The modifications made in the system are modified after restarting the system. This kind of environment is more secure and is useful in enterprise/commercial usages. E.g. Microsoft Virtual Server, VMware ESX Server, and Xen.
There are several different pieces of software that handle the task of virtualization.