The VPS have the same operation as that of a dedicated server, they have guaranteed minimum resources so that if a VPS exceeds the amount of RAM or CPU memory assigned, it will not affect the operation of the other VPS hosted on the same machine.
If you didn’t understand it, we could abbreviate that a dedicated server is divided into several parts and each part is a VPS.
Should you use VPS?
It depends on how many websites you have and their traffic. As a general rule, there are usually three sections that webmasters go through:
Shared Hosting > VPS > Dedicated Server.
If you are in a shared hosting and you are noticing that website is consuming too many resources, or loading slow then you should consider moving to VPS. But before making final decision you should consider following points;
That you have updated all the scripts (forums / blogs / content managers …) to the latest version
Disable the add-ons (“Add-ons” or “Plugins”) that you don’t use or you can do without its functionalities
Optimize your databases
Use caching systems (eg for Wordpress: WP-SuperCache)
If all this didn’t work, you probably need to jump into a VPS.
"Managed" or “Not Managed”?
Managed: the company’s own technicians will solve any problem with your VPS; Apache configuration, MySQL, PHP, optimizations, security checks, application installation, 24-hour monitoring of services and their status, etc.
Not managed: the technical service will only guarantee the contracted resources, if you have problems with the VPS you must solve them yourself or hire a sysadmin (systems administrator) to do the work for you.
Managements are generally more expensive but definitely recommended if you have little or no idea about managing servers. Otherwise, or if you like adventure and you are one of those who learn from mistakes, you have the unmanaged ones.
Root access. Yes or no?
Root access is full access to the VPS via SSH (console). You can modify any configuration of all applications (web server / database / ftp, …), install applications, etc. All unmanaged plans include root access and some managed plans as well.
Note: Just because you don’t have root access on a managed VPS doesn’t mean it’s limited, you can ask your support to install applications for you or make the modifications you consider appropriate.
That’s it for little guide. If there is any error do not hesitate to correct it.