The availability of a website is measured by the percentage of a year in which the website is publicly accessible and reachable via the Internet. This is different from measuring the uptime of a system. Uptime refers to the system itself being online. Uptime does not take into account being able to reach it as in the event of a network outage. A hosting provider's Service Level Agreement (SLA) may include a certain amount of scheduled downtime per year in order to perform maintenance on the systems. This scheduled downtime is often excluded from the SLA timeframe, and needs to be subtracted from the Total Time when availability is calculated. Depending on the wording of an SLA, if the availability of a system drops below that in the signed SLA, a hosting provider often will provide a partial refund for time lost. How downtime is determined changes from provider to provider, therefore reading the SLA is imperative. Not all providers release uptime statistics. Most hosting providers will guarantee at least 99.9% uptime which will allow for 43m of downtime per month, or 8h 45m of downtime per year.
You could think of the sites that share your server as your roommates; there's really not that much separating you from them. Sure, you can close the bedroom door, but they can still cause nightmares for you in the kitchen and the bathroom. In web hosting terms, all the sites share a single server's resources, so huge traffic spike on Site A may impact the neighboring sites' performances. It's even possible that another site could take down the shared server altogether, if it crashed hard enough.
Virtual private server (VPS) or cloud hosting can be a good middle-of-the-road option between the lowest pricing (shared servers) and highest reliability (dedicated servers). A VPS is a physical server that usually has multiple sites hosted on it. However, it’s much more sophisticated than shared servers in its ability to distribute server resources – and it carries a lighter price tag than for dedicated hosting.
The user gets his or her own Web server but is not allowed full control over it (user is denied root access for Linux/administrator access for Windows); however, they are allowed to manage their data via FTP or other remote management tools. The user is disallowed full control so that the provider can guarantee quality of service by not allowing the user to modify the server or potentially create configuration problems. The user typically does not own the server. The server is leased to the client.
The company doesn't list a virtual private server offering, but it bills its Elastic Sites service as a VPS alternative, offering the ease of use of a simple shared hosting plan and the performance and scalability of a VPS. GlowHost also offers a number of different cloud hosting plans, with special attention to providing enterprise-grade services.
Until 1991, the Internet was restricted to use only "...for research and education in the sciences and engineering..." and was used for email, telnet, FTP and USENET traffic—but only a tiny number of web pages. The World Wide Web protocols had only just been written and not until the end of 1993 would there be a graphical web browser for Mac or Windows computers. Even after there was some opening up of internet access, the situation was confused until 1995.
Hosting that is aimed at specific CMS platforms and tweaked optimally for them: e.g., WordPress hosting, Drupal hosting, Magento hosting, etc. In these cases, the best hosts do far more than just provide the minimal requirements for those platforms. They provide a rich, and fully managed environment so your site can perform like a well-tuned machine.