In 2010, Gmail was available 99.984 percent of the time, for both business and consumer users. 99.984 percent translates to seven minutes of downtime per month over the last year. That seven-minute average represents the accumulation of small delays of a few seconds, and most people experienced no issues at all. For those few who were disrupted for a longer period of time, we're very sorry, and Google Apps for Business customers received compensation where appropriate. We're particularly pleased with this level of reliability since it was accomplished without any planned downtime while launching 30 new features and adding tens of millions of active users.

Seven minutes of downtime compares very favorably with on-premises email, which is subject to much higher rates of interruption that hurt employee productivity. The latest research from the Radicati Group found that on-premises email averaged 3.8 hours of downtime per month. In comparison to Radicati's metrics for on-premises email, our calculations suggest that Gmail is 32 times more reliable than the average email system, and 46 times more available than Microsoft Exchange.