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Distributed operating systemsEvery time a client runs, on the first attempt to use a server, the client sends a query message to a special mapping server, often called a name server, asking it for the machine number where the server is currently located. Once this address has been obtained, the request can be sent directly. As in the previous case, addresses can be cached. In summary, we have the following methods for addressing processes: 1. Hardwire machine.number into client code. 2. Let processes pick random addresses; locate them by broadcasting. 3. Put ASCII server names in clients; look them up at run time. Each of these has problems. The first one is not transparent, the second one generates extra load on the system, and the third one requires a centralized component, the name server. Of course, the name server can be replicated, but doing so introduces the problems associated with keeping them consistent. A completely different approach is to use special hardware. Let processes pick random addresses. However, instead of locating them by broadcasting, the network interface chips have to be designed to allow processes to store process addresses in them ...» |
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