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316 Part 2 ½ Regions of Computer Space

Section ½ 3 Concurrency: Single-Processor System

lines. On these lines, the members of the "net" can transmit information-usually in the form of programs, data, or messages. The link performs an information switching function and is handled by an interface message processor (IMP) and a network control program stored within each member installation's "host" computer. Each IMP operates in a "store and forward mode," that is, information in one IMP is not lost until the receiving IMP has signalled complete reception and retention of the message. The IMP interfaces with each member's computer system and converts information into standard format for transmission to the rest of the net. Conversely, the IMP accepts information in a standard format and converts it to the particular data format of the member installation. In this way, the ARPA network is a form of a computer utility with each contributing member offering its unique resources to all of the other members. The Illiac IV system then is an ARPA network resource that will be shared by the members of the ARPA network; even the host site of the Illiac IV, Ames Research Center at Moffett Field, Calif., will be constrained to access Illiac IV via the ARPA network.



Bouknight, Denenberg, McIntyre, Randall, Sameh, and Slotnick [1972]; Barnes, Brown, Kato, Kuck, Slotnick, and Stokes [1968]; Denenberg [1971]; "Electronic Computers" [1969]; Slotnick [1967]; Slotnick [1971]; Slotnick, Borck, and McReynolds [1962].

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