With a Dedicated (real, physical) server, you own or rent a physical box of hardware and have exclusive use of it. This means you can specify exactly what speed and type of CPU, what type and size of disk and how much memory it should have and so on. All the resources, including the CPU, are exclusively for your own use. This means that no matter what another customer buying or renting a similar server to yours might do with theirs, there will be no impact on the performance of your server.
With a Virtual Private Server (VPS) - also sometimes called a Virtual Dedicated Server - you rent what is in effect a self-contained subdivision of a physical server, with one or more other customers also renting similar subdivisions and all making use of the same physical memory, physical disks, physical network interfaces etc. The self-contained subdivisions that form the basis of a VPS are sometimes called Containers, Instances or Virtual Environments (VEs).
Each VPS acts almost exactly like a Dedicated (physical) server - they have their own private allocation of disk space which no other VPS can access, can make use of a minimum amount of RAM (known as Guaranteed RAM), run their own operating systems and software which can be different from VPS to VPS, can be individually rebooted, backed up and restored, and allow full root access.
But although you can specify the relative amount of CPU power that a VPS has access to compared to other VPSes running on the same physical server, you cannot be absolutely sure exactly how much CPU power your VPS will be given at any particular moment*. The virtualisation software (in our case Parallels Virtuozzo Containers) used to create and manage the VPSes running on the physical server will, however, make sure that CPU and memory resources will be allocated fairly, and that customers opting for more powerful VPSes will have access to more CPU resources than those with less powerful VPSes. This is achieved through the use of CPU weighting (Please see the Additional Details and FAQs page for more information). CPU weighting also ensures that very busy VPSes running on the same physical server as your VPS will not stop your VPS from working completely and will instead share out the CPU power available on the physical server fairly.
A similar situation applies to disk, memory and other shared physical resources - for example if other VPSes need to do a great deal or reading or writing from disk or memory at the same time as yours does, it will impact the performance of all VPSes. But again the Virtuozzo virtualisation software will ensure that each VPS gets a fair share of the physical resources available in order to make sure that particularly busy VPSes are not allowed to consume all available resources at the total expense of all other VPSes.
* This is technically possible, but it is rarely implemented on VPS products offered to customers for hosting etc
To upgrade a physical Dedicated Server it is normally necessary to switch it off and install additional or replacement hardware. In the case of adding larger disks it may be necessary to copy the data held on the original disks or even to re-install the operating system and restore a backup copy of the data on the original disks. It may even be necessary to upgrade to a completely new Dedicated Server in order to gain more processing power.
Unlike a physical server, a VPS can be upgraded (or downgraded) in a matter of minutes, without you having to re-install the operating system or any data, and normally without any downtime. If you need more disk space, memory or even CPU power, we can allocate more to your VPS with the press of a few keys and it is instantly available.
There can be times when you need to start afresh and re-install the operating system from scratch. With a normal Dedicated Server this usually involves a great deal of time and effort (though some Dedicated Server Providers, including Cymru 1, have an automated system to make this process less painful). All your data is normally lost during an operating system re-install.
With a VPS, however, re-Imaging (wiping clean and re-installing the operating system) can be achieved in a matter of minutes rather than hours, and is completely automated. In fact you can do it yourself through the Parallels Power Panel (PPP), an easy to use, web-based VPS control panel. You also have the option of retaining a copy of your original files and data, though keep in mind that this will be accessible via a special directory within the file system of your VPS - the files and data is not left in situ as this could lead to version conflicts and configuration errors. Please also note that if you re-image a VPS that has certain optional extras, such as Atomic Security, or you have chosen the Server Management option, you will be charged a fee of £50 + VAT to re-install and re-configure these options.
The Parallels Power Panel (previously known as the Virtuozzo Power Panel) also allows you to start, stop and restart (reboot) your VPS, manage services and processes running in your VPS, monitor VPS resource utilization for CPU, system and disk space, back up and restore your VPS and view logs to monitor resource shortage alerts. It also includes an embedded SSH client for easy root access, though you can use a conventional SSH client if you need to.
Dedicated Servers usually come with nothing but an operating system installed. If you intend to use your dedicated server for hosting, you'll therefore need to rent (or purchase), install and configure your own hosting control panel - or make all changes manually. With our VPS options, however, you don't need to worry about this - we include the Plesk control panel as standard, pre-installed and ready to be used. Plesk is available pre-installed on our range of Dedicated Servers too, but at additional cost.
On a physical server, because you don't share anything at all with anybody else, you can do pretty much anything you want with no limitations of any sort (Terms and Conditions of your contract permitting, of course)
This is not always the case with a VPS. For example, due to way in which Virtuozzo works, you will not be able to build or use your own Linux Kernel on a VPS -- all VPSes run on a single, shared kernel - and certain hardware registers, such as the hardware clock, are read-only. In addition, extremely timing-sensitive applications, such as Digium's Asterisk, may not function correctly. And for those Linux distributions that support it on a physical server, please note that selinux and similar functionality is not available in a Virtuozzo VPS.
The bottom line is really that if you need to do something particularly complicated or have very specialist needs, a Dedicated Server is the best option - a VPS may not be suitable. .
But if you just need to host websites, process email, store data, set up an online collaboration service or just to experiment then a VPS is ideal and will normally be a great deal more cost-effective than a Dedicated Server.