Hosting Uptime and Reliability-99% uptime Guarantee? Is it real?

Hosting uptime refers to the percentage of time the host is accessible.

Many hosting companies claim that they have a 99.9% uptime, but can this be trusted? What if a server restarts? What if there is a a physical problem, or in the unlikely event that there is sep 11 blast?

What if they are doing a maintenance job?

They claim only refers to a server being powered on and doesn't account for network downtime and other downtime. Real downtime can potentially be larger than the percentage guaranteed by the provider. Many providers tie uptime, and accessibility, into their own Service Level Agreement, or SLA. SLAs may or may not include refunds, or reduced costs if performance goals are not met.

One should be very careful to choose a trusted web hosting company, reliable and good uptime that is realistic.