Both the servers are a type of hosting services provided by web hosting organizations and both the servers are unique in their own way. As the VPS can be used by low and medium-sized websites and dedicated server can be used by big websites. They are almost same, as long as the VPS is a container on hardware based virtualization (HVM) or kernel based virtualizaton (KVM). In this type of virtualization, a dedicated amount of memory is assigned to the VPS which can be used by the guest operating system same as the dedicated server.
Managing more websites with less ram, is something that depends on the memory consumption of the websites that you are going to host on your server.
or check more about VPS and Dedicated Server i found the Wikipedia link on the Internet: