Like scalability, availability is a key concern for users in small and medium-sized businesses as well as in large enterprise organizations. As businesses of all sizes become increasingly web based and globally oriented, computing services must be able to respond 24 hours a day and 365 days a year, placing a premium on reduced downtime. UNIX systems are being used to host increasingly critical workloads in many environments, and in response, the developers of UNIX products are implementing functions at multiple levels to help maintain uptime. In many cases, the developers have drawn on techniques that have traditionally been implemented in mainframes.

With UNIX systems, functional advances to boost uptime have been concentrated in three areas: dynamic reconfiguration (i.e., the ability for operating systems to adapt to the addition and removal of CPU and memory resources without requiring a reboot); error handling architectures (which help application and higher-level service infrastructures correctly adapt when failures occur in hardware or lower-level software); and High Availability and Disaster Recovery tools (which enable workloads to migrate to backup hosts when primary hosts fail.)

Click on one of the links below to see how the UNIX systems compare in each of these areas:

	Dynamic Reconfiguration (9 ratings)
	Error Recovery (9 ratings)
	HA Cluster & DR Options (3 ratings)