Abstract: In a system such as a multiple computer system where memory locations (A, B, C) can be substantially simultaneously updated from difference sources, an updating count (C, C1) is provided indicative of the sequence of each updating message or signal (195, 295) in a stream of such updating messages or signals. The updating count is stored in a counter. To reduce the storage requirements for the counter and the bandwidth requirements for the updating messages including the count value, small count values are utilized. From time to time sending of updating messages is halted and the count values re-set to avoid arithmetic overflow.

Abstract: A multiple computer system is disclosed in which n computers (M1, M2 . . . Mn) each run a different portion of a single application program written to execute only on a single computer. The local memory of each computer is maintained substantially the same by updating all computers with every change made to addressed memory locations. Contention can arise when the same memory location is substantially simultaneously updated by two or more machines because of transmission delays and latency of the communications network interconnecting all the computers. In particular a method of detecting and resolving contention is disclosed which utilizes a count value indicative of the number of the sequence of occasions on which each memory location has been updated. Contention is indicated if the currently stored count value and the incoming updating count value are the same. The contention can be resolved by providing a further rule.

Abstract: A switching network for multiple computer systems is disclosed which utilises pairs of multi-port switches (S1-S4) and (preferably) less complex switches (S5-S7). The multi-port switches are arranged in pairs with a computer of the multiple computer system being able to be connected to each port of each multi-port switch except for one port. That one port of each multi-port switch is connected to a single one of the less complex switches. All the less complex switches are arranged in a twin branch multi-level tree structure. The arrangement overcomes bottlenecks arising from the serial interconnection of multi-port switches.

Abstract: A multiple computer system is disclosed in which the local memory of each computer (M1, M2, . . . Mn) can be different having some memory locations (A, B) which are replicated in other computers and other memory locations (E) which are not. When any computer seeks to acquire or release a synchronizing lock a check (171, 181) is made to see if the relevant memory location is present on any other machine. If yes, synchronization is carried out.

Abstract: A switch protocol for network communications (particularly but not exclusively for multiple computer systems) is disclosed in which each switch (S1, S2, S3) maintains a list of addresses which can be reached via each port (A,B,C) of the switch. In addition, prior to delivering a message or packet to a port, the switch deletes any address in the message or packet which is unable to be reached via that port. The arrangement saves the repetitive sending of uni-cast messages and also saves broadcast messages being sent via the switches to computers which are not intended to receive the messages.

Abstract: The addition of one or more additional computers to a multiple computer system having replicated shared memory (RSM) or partial or hybrid RSM, is disclosed. The or each additional computer (M4) has its independent local memory (502) initialised by the system to at least partially replicate the independent local memory of the computers (M1-M3) of the multiple computer system.

Abstract: A multiple computer system is disclosed in which n computers (M1, M2 . . . Mn) each run a different portion of a single application program written to execute only on a single computer. The local memory of each computer is maintained substantially the same by updating all computers with every change made to addressed memory locations. Contention can arise when the same memory location is substantially simultaneously updated by two or more machines because of transmission delays and latency of the communications network interconnecting all the computers. In particular a method of broadcast memory updating with contention detection and resolution is disclosed which utilizes either a single or plural count value(s) and/or single or plural resolution value(s) for multiple memory locations. The count value is indicative of the number of the sequence of occasions on which a memory location has been updated.

Abstract: A multiple computer environment is disclosed in which an application program executes simultaneously on a plurality of computers (M1, M2, . . . Mn) interconnected by a communications network (3) and in which the local memory of each computer is maintained substantially the same by updating in due course. A lock mechanism is provided to permit exclusive access to an asset, object, or structure (ie memory location) by acquisition and release of the lock. In particular, before a new lock can be acquired by any other computer on a memory location previously locked by one computer, any updating count(s) for the previously locked memory location are transmitted to all the other computers and their corresponding memory locations (before the in due course updating). Thus the lock acquiring computer can ascertain if its local memory has been adequately updated.