what is the difference between them or they are same ?
The difference is simple. A dedicated server typically means your server is running directly on physical hardware. A VPS means your server is a virtual instance running on physical hardware. That same set of physical hardware can be running other virtual instances at the same time depending on the provider's allocations.
As for how they perform... a dedicated server will always be a constant amount of performance... where a virtual instance can vary greatly depending on the provider, and other users sharing the physical hardware.
A dedicated server (usually a lot more expensive) is a single server you rent. you get root access and need to take care about everything on the machine, including security patches, backup, etc... A Virtual Private Server is usually a virtualized Guest machine on a server. Depending on the price you pay, you get a slice of the Host machines resources for your VPS. The provider is able to change your resources (memory, ram, cpu) dynamically and you pay the cost accordingly. The resources are limited. It is possible to run 20+ VPS on a single server, depending on its size. Because of this things a VPS is a lot cheaper than a dedicated server. Important is that usually the provider cares about security, backup, etc. Third type would be a managed server, a dedicated server for you managed by the provider. More expensiv than dedicated server.
The differences between VPS and shared hosting include the following:
- On a VPS, you have dedicated resources (RAM, CPU, etc.), while on shared hosting you share these resources with many other websites/users.
- VPS servers (usually) require more setup and configuration, while shared servers are pretty much set up for you already.
- On a VPS, you get complete root access, while on a shared server you do not.
- On a VPS you will get a dedicated IP address and nameserver(s).
- VPS servers tend to be more secure.
- VPS servers are considerably more expensive.
There are many other differences as well; these are just a few of the main ones.