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1.1 ! root 1: .\" Copyright (c) 1983 Regents of the University of California. ! 2: .\" All rights reserved. The Berkeley software License Agreement ! 3: .\" specifies the terms and conditions for redistribution. ! 4: .\" ! 5: .\" @(#)2.0.t 6.2 (Berkeley) 5/12/86 ! 6: .\" ! 7: .ds ss 1 ! 8: .sh "System facilities ! 9: This section discusses the system facilities that ! 10: are not considered part of the kernel. ! 11: .PP ! 12: The system abstractions described are: ! 13: .IP "Directory contexts ! 14: .br ! 15: A directory context is a position in the UNIX file system name ! 16: space. Operations on files and other named objects in a file system are ! 17: always specified relative to such a context. ! 18: .IP "Files ! 19: .br ! 20: Files are used to store uninterpreted sequence of bytes on which ! 21: random access \fIreads\fP and \fIwrites\fP may occur. ! 22: Pages from files may also be mapped into process address space.\(dg ! 23: A directory may be read as a file. ! 24: .FS ! 25: \(dg Support for mapping files is not included in the 4.3 release. ! 26: .FE ! 27: .IP "Communications domains ! 28: .br ! 29: A communications domain represents ! 30: an interprocess communications environment, such as the communications ! 31: facilities of the UNIX system, ! 32: communications in the INTERNET, or the resource sharing protocols ! 33: and access rights of a resource sharing system on a local network. ! 34: .IP "Sockets ! 35: .br ! 36: A socket is an endpoint of communication and the focal ! 37: point for IPC in a communications domain. Sockets may be created in pairs, ! 38: or given names and used to rendezvous with other sockets ! 39: in a communications domain, accepting connections from these ! 40: sockets or exchanging messages with them. These operations model ! 41: a labeled or unlabeled communications graph, and can be used in a ! 42: wide variety of communications domains. Sockets can have different ! 43: \fItypes\fP\| to provide different semantics of communication, ! 44: increasing the flexibility of the model. ! 45: .IP "Terminals and other devices ! 46: .br ! 47: Devices include ! 48: terminals, providing input editing and interrupt generation ! 49: and output flow control and editing, magnetic tapes, ! 50: disks and other peripherals. They often support the generic ! 51: \fIread\fP and \fIwrite\fP operations as well as a number of \fIioctl\fP\|s. ! 52: .IP "Processes ! 53: .br ! 54: Process descriptors provide facilities for control and debugging of ! 55: other processes. ! 56: .ds ss 2
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