Business continuity encompasses activities that an enterprise performs to maintain timeliness, consistency, and availability of its data, operations, and services. Application availability depends upon the ability of IT services to survive any fault, whether it is a server failure, a network fault, or a data center disaster. Data availability depends on the existence of up-to-date backup data copies. Data replication is an enabling technology for achieving high or continuous availability for application services and the timely backup of important data. There are two primary data replication technologies, hardware replication and software replication. In this article, these two technologies are compared, concluding that a business continuity architecture built on software-based transactional data replication is the only viable solution to meet the highest levels of service availability and protection against data loss for mission-critical applications.