A continuously available computer system is characterized as having essentially no downtime in any given year. A system with 99.999% availability experiences only about five minutes of downtime. In contrast, a high availability system is defined as having 99.9% uptime, which translates into a few hours of planned or unplanned downtime per year.
With any IT system it is desirable that the system and its components (be they hardware or software) are up and running and fully functional for as long as possible, at their highest availability. The most desirable high availability rate is known as "five 9s", or 99.999% availability.
can offer high availability for all major Internet services like web, email, dns, sql, etc.