Abstract: A method of controlling communication between a head-end system and a number of client systems through a network, wherein, for each receiver, only a nearest one of the multicast router systems in the network is configured to forward a copy of a message addressed to the multicast groups of which the receiver is a member directly to the receiver, includes:maintaining subscriber group information linking each registered one of the number of client systems to an associated one of a plurality of subscriber groups, and allocating registered client systems to at least one multicast group, such that all client systems associated with a particular subscriber group are in a common multicast group. Information uniquely identifying the nearest multicast router system nearest to a receiver for a first client system is obtained, and the first client system is assigned to a subscriber group including at least one further client system having the same nearest multicast router system.

Abstract: A method is described of providing patches for software installed on a plurality of client systems. The method may include obtaining computer program code for inclusion in a patch, the code being arranged to co-operate with at least part of the software installed on a client system to perform a certain function after a patch has been applied in the client system. A first patch for application may be provided in at least one first client system with an instruction to update the actual patch level maintained in the client system to reflect a next level. The method may provide a second patch for at least one other of the client systems with an instruction to update the actual patch level maintained in the client system to reflect the next level. The code may be provided only in the first of the first and second patches.

Abstract: A method of external data storage in a system including a primary processing device, having a processor and a primary data storage unit, adapted to run application programs for processing active records in the processor and configured to store data belonging to active records in the primary data storage unit; and a secondary data storage system, accessible to the primary processing device, includes loading data belonging to an active record into the primary data storage unit and externalising the record by transferring at least a piece of data belonging to the record to the secondary data storage system for storage. The step of externalising a record includes the making of a call by an application program using data belonging to the record to an interface, arranged to transfer the piece of data to the secondary data storage system.