messages can be sent across a channel set to a fast mode, in which delivery is not assured in the event of a channel failure. MQ supports both circular and linear logging. Retrieving messages from queues Information can be retrieved from queues either by polling the queue to check for available data at suitable intervals, or alternatively MQ can trigger an event, allowing a client application to respond to the delivery of a message. Availability IBM MQ offers a variety of solutions to cater for availability: Replicated Data Queue Manager (RDQM / 'Easy HA'- MQ Advanced on distributed only): Synchronous replication between three servers that all share a floating IP address. Queue Manager Clusters: Groups of two or more queue managers on one or more computers are defined to a cluster, providing automatic interconnection, and allow queues to be shared among them for load balancing and redundancy. Queue Sharing Groups (z/OS only): In a Shared Queue environment, an application can connect to any of the queue managers within the queue-sharing group. Because all the queue managers in the queue-sharing group can access the same set of shared queues, the application does not depend on the availability of a particular queue manager. This gives greater availability if a queue manager stops because all the other queue managers in the queue-sharing group can continue processing the queue. Multi-Instance Queue Managers (available from v7.0.1): Instances of the same queue manager are configured on two or more computers with their queues and meta data residing on shared storage. By starting multiple instances, one instance becomes the active instance and the other instances become standbys. If the active instance fails, a standby instance running on a different computer automatically takes over. History Version release dates Version end of support dates The following table applies to MQ software. The MQ Appliance has different lifecycle dates for both firmware and hardware than those in the table. Background architectural reference With the advent of computers, IBM saw an opportunity to apply new technology to the need for message switching. In the early 1960s, IBM marketed the IBM 7740 Communication Control System and the IBM 7750 Programmed Transmission Control, which were programmable message switching systems. The IBM System/360 was announced in April 1964 and with it came communication access methods such as BTAM and QTAM (Basic and Queued Telecommunications Access Methods). In 1971, TCAM, the Telecommunications Access Method, offered