People often don't know the difference between different hosting options, so here are explanations of different hosting options.
Regular Shared Hosting:
All the cpu, memory, drive space, and bandwidth are shared on a server. They all use the same operating system, use the same services, like the mail server, mysql server, apache, php, etc. One site can hog the resources and affect the performance of other sites. Each hosting account will have its own control panel and normally you can have additional addon domains within that hosting account. No server management is required.
Similar to Regular Shared Hosting with the exception that each hosting account is self-contained and is allotted a certain amount of CPU useage. Memory can also be allotted, but, it is disabled on our servers as we've found memory useage not to be a problem. One site won't affect the performance of another site. If a site starts using all its CPU cycles, then the site will slow down and eventually start throwing "internal server" errors. No server management is required.
Anothe benifit over a VPS and Dedicated, is there are still "shared" resources. mySQL and the mail server usage, for example, aren't counted against your CPU limitations.
A VPS (virtual private server) is like a mini dedicated server. One full dedicated server can have multiple VPS servers on it. Each VPS is self contained and has it's own operating system, WHM/cPanel, mysql, mail server, etc. The VPS will have X number of CPUs XXX amount of Ram, and XX amount of drive space assigned to it. One VPS will not affect the performance of other VPS's on the server. WHM (WebHostingManager) allows you to create multiple cPanel hosting accounts and is limited only by the resources assigned to the VPS. Like a fully dedicated server, a new VPS must be set up and configured, which often includes configuring WHM, hardening the server, setting up nameservers, configuring mysql/exim etc, installing a firewall, hardening the VPS for security, etc. One hosting account within the VPS can affect the performance of other hosting accounts within the VPS.
CPU and memory can often be instantly upgraded, requiring only a restart. Server management is required either by the client or the provider (normally extra) for initial server configuration and ongoing routine maintenance.
VPS/Semi-Dedicate/Cloud Server are basically the same. A cloud server will often have drive space independent of the server on a SANS array where the VPS/Semi-Dedicated will use the server's drive space it is located on.
A dedicated server is assigned to one client and the number of hosting accounts is limited only by the server's resources. CPUs are not normally upgradeable. Ram is normally upgradeable but requires the server to be taken off line and physically installed. One hosting account can affect the performance of another hosting account. Server management is required as with the semi-dedicated.