An I/0 system has been implemented in the Multics system that facilitates dynamic switching of I/0 devices. This switching is accomplished by providing a general interface for all I/O devices that allows all equivalent operations on different devices to be expressed in the same way. Also particular devices are referenced by symbolic names and the binding of names to devices can be dynamically modified. Available I/0 operations range from a set of basic I/0 calls that require almost no knowledge

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... of the I/O System or the I/0 device being used to fully general calls that permit one to take full advantage of all features of an I/O device but require considerable knowledge of the I/0 System and the device. The I/O System is described and some popular applications of it, illustrating these features, are presented.