Business continuity is part of ITSM methodology related to nondisruptive opperation of the ICT systems. This is achieved by means of High Availability (HA) and Disaster Recovery (DR). High Availability refers to a system or component that is continuously operational for a desirably long time period. Availability can be measured relative to "100% operational" or "never failing." A widely-held but difficult-to-achieve standard of availability for a system or product is known as "five 9s" (99.999 percent) availability.