Basicly, Dedicated Server = 1 os on one machine where as VPS is a virtual server, and you can have several virtual machines on one physcial machine, meaning you can have 2 physical servers, but 10 virtual servers (the only different is the amount of resouces they can use)
* User-mode Linux * vmware * Microsoft Virtual Server * qemu * VDSmanager * Virtualbox * xensource * parallels * OpenVZ * HyperVM * Virtuozzo * FreeVPS * Solaris Containers (Zones) Take your pick. http://en.wikipedia.org/wiki/Virtual_private_server
Definition : Virtual Private Servers is means of splitting a single physical server into multiple virtual servers. Virtual private servers are also referred to as Virtual Dedicated Server or Virtual Server and abbreviated VPS or VDS . The practice of splitting single server into multiple servers was common practice in the days of mainframe computers, but has seen a resurgence lately with the development of software such as User-mode Linux and Xen. Software Requirements for using VPS : The Hardware Node should run either on Red Hat Enterprise Linux 3 or 4, or Fedora Core 3 or 4, or CentOS 3.4 or 4. This requirement does not restrict the ability of OpenVZ to provide other Linux versions as an operating system for Virtual Private Servers. The Linux distribution installed in a Virtual Private Server may differ from that of the host OS. Hardware Requirements for using VPS : The Hardware Node requirements for the standard 32-bit edition of OpenVZ are : 1) Firstly, the computer should satisfy the Red Hat Enterprise Linux or Fedora Core hardware requirements. 2) IBM PC-A compatible computer is recommended. 3) CPUs: CPU used for VPS would be Intel Celeron, Pentium II, Pentium III, Pentium 4, Xeon, or AMD Athlon CPU. The more Virtual Private Servers you plan to run simultaneously, the more CPUs you need. 4) Memory: Minimum 128 MB of RAM. The more memory, the more Virtual Private Servers you can run. The exact figure depends on the number and nature of applications you are executing in your Virtual Private Servers. However, on the average, at least 1 GB of RAM is always preferable for every 20-30 Virtual Private Servers. 5) Hard Disk Drive: Minimum 4 GB of free disk space is recommended. Each Virtual Private Server occupies 400-600 MB of hard disk space for system files in addition to the user data inside the Virtual Private Server. It should be considered while planning disk division and the number of Virtual Private Servers to run. 6) NIC: Network card will be either Intel EtherExpress100 (i82557-, i82558- or i82559-based) or 3Com(3c905 or 3c905B or 3c595) or RTL8139-based are always preferable.A typical two-way Dell PowerEdge 1650 1u-mountable server with 1 GB of RAM and 36 GB of hard drives is suitable for hosting 30 Virtual Private Servers. __________________