A return value of indicates an error and a return

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Unformatted text preview: t clients and servers are processes, and not machines, or hosts as they are often called in this context. A single host can run many different clients and servers concurrently, and a client and server transaction can be on the same or different hosts. The client-server model is the same, regardless of the mapping of clients and servers to hosts. 12.2 Networks Clients and servers often run on separate hosts and communicate using the hardware and software resources of a computer network. Networks are sophisticated systems and we can only hope to scratch the surface here. Our aim is to give you a a workable mental model from a progammer’s perspective. To a host, a network is just another I/O device that serves as a source and sink for data, as shown in Figure 12.2. An adapter plugged into an expansion slot on the I/O bus provides the physical interface to the network. Data received from the network is copied from the adapter across the I/O and memory buses into memory, typically by a DMA transfer. Similarly, data can also be copied from memory to the network. Physically, a network is a hierarchical system that is...
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