UPTIME What Uptime stands for? Uptime is a measure of the time a server has been running without any downtime. Why it is counted in percentage? Usually hosting companies mention their server’s uptime in percentage such as 99,9% or 99,99% and so on. This is automatically calculated according the downtime per specific time period. On the above table you can see some examples: Availability % Downtime per year Downtime per month 99% 3.65 days 7.20 hours 99.5% 1.83 days 3.60 hours 99.8% 17.52 hours 86.23 minutes 99.9% 8.76 hours 43.8 minutes 99.95% 4.38 hours 21.56 minutes 99.99% 52.56 minutes 4.32 minutes Is there uptime of 100%? No, there is no server being available for 365 days per year. Even if you can find uptime of 100% in one month period, it will be hard to find uptime of 100% during a year or forever. Servers even if they do not have failures, they need updates and restarts, which result in some minutes of downtime thus the percentage cannot be 100%. Is 99.99% the same with 99.9%? No! 99.9% is the same with 99.90%. As you can see on the table, in one month period 99.9% uptime means almost 9 hours of downtime, while 99.99% uptime means almost 1 hour of downtime. So be careful on reading the numbers. Should I go with a hosting company that promise 99.9% uptime? If they guarantee 99.9% uptime, it means they may offer even better uptime such as 99.97%. The number can vary from 99.90% up to 99.99%. So, before registering with them, ask for uptime charts. Are there third-party uptime checkers? Yes there are many uptime checkers such as: www.pingdom.com http://www.webhostingstuff.com/ www.site-uptime.net and so on. So take this advice: Before choosing a web hosting company, be sure to ask for the uptime history charts from third-parties for the specific server that they are going to host your sites. Check the table and then you can decide if their downtime is affordable for your requirements. Source: http://en.wikipedia.org/wiki/High_availability An example of uptime calculator: http://easyuptimecalc.com/index.php