Most logical operations and data processing occur in parallel on multiple bits simultaneously. Microprocessors, for example, have wide data buses to increase throughput. With wide buses comes a requirement for more wires to connect the logical elements in a system. The interconnection penalty increases as distances increase. Within a chip, the penalty is small, and wide buses are common. Implementing wide buses on a circuit board is also common because of the relatively short distances involved.
The economics and technical context of interconnect changes as soon as the distances grow from
centimeters to meters to kilometers. Communication is primarily concerned with transporting data from one location to another rather than processing that information as it is carried on a wire. With distance comes the expensive problem of stringing a continuous wire between two locations. Whether the wire is threaded through a conduit between floors in an office, buried under the street between buildings, or virtually constructed via radio transmission to a satellite, the cost and complexity of connecting multiple wires is many orders of magnitude greater than on a circuit board. Serial communication is well suited to long distances, because fewer wires are used as compared to a parallel bus. A serial data link implies a single-wire medium, but there can be multiwire serial links as well and consumers of the data that operate using a parallel bus. A
transceiver converts between a parallel bus and a serial stream and handles any link-level timing necessary to properly send and receive data. A transducer , or modulator in wireless links, converts between the medium’s electromagnetic signaling characteristics and the transceiver’s logic-level signals. Finally, a conductive path joins the two transducers. This path can be copper wire, glass fiber optic cable, or free space. These logical components may be integrated in arbitrary physical configurations in different implementations, so not all serial links will consist of three specific discrete pieces. Simple links may have fewer pieces, and complex links may have more.
The total cost of a data link is the sum of the cost of the transceiver/transducer subsystems at each end and the cost of the physical medium itself. A serial port on a desktop computer is inexpensive because of its relatively simple electronic circuits and because the medium over which it communicates, a short copper wire, is fairly cheap. In contrast, a satellite link is very expensive as a result of the greater complexity of the ground-based transmission equipment, the high cost of the satellite itself, and the licensing costs of using the public airwaves. If only one bit is transferred per clock cycle in a serial link, it follows that either the serial bit clock has to be substantially faster than the parallel bus, or the link’s bandwidth will be significantlybelow that of the parallel bus. Bandwidth in a communication context refers to the capacity of the communications channel, often expressed either in bits-per-second (bps) or bytes-per-second (Bps). Serial links are available in a broad spectrum of bandwidths, from thousands of bits per second (kbps) to billions of bits per second (Gbps) and are stretching toward trillions of bits per second (Tbps)!
The economics and technical context of interconnect changes as soon as the distances grow from
centimeters to meters to kilometers. Communication is primarily concerned with transporting data from one location to another rather than processing that information as it is carried on a wire. With distance comes the expensive problem of stringing a continuous wire between two locations. Whether the wire is threaded through a conduit between floors in an office, buried under the street between buildings, or virtually constructed via radio transmission to a satellite, the cost and complexity of connecting multiple wires is many orders of magnitude greater than on a circuit board. Serial communication is well suited to long distances, because fewer wires are used as compared to a parallel bus. A serial data link implies a single-wire medium, but there can be multiwire serial links as well and consumers of the data that operate using a parallel bus. A
transceiver converts between a parallel bus and a serial stream and handles any link-level timing necessary to properly send and receive data. A transducer , or modulator in wireless links, converts between the medium’s electromagnetic signaling characteristics and the transceiver’s logic-level signals. Finally, a conductive path joins the two transducers. This path can be copper wire, glass fiber optic cable, or free space. These logical components may be integrated in arbitrary physical configurations in different implementations, so not all serial links will consist of three specific discrete pieces. Simple links may have fewer pieces, and complex links may have more.
The total cost of a data link is the sum of the cost of the transceiver/transducer subsystems at each end and the cost of the physical medium itself. A serial port on a desktop computer is inexpensive because of its relatively simple electronic circuits and because the medium over which it communicates, a short copper wire, is fairly cheap. In contrast, a satellite link is very expensive as a result of the greater complexity of the ground-based transmission equipment, the high cost of the satellite itself, and the licensing costs of using the public airwaves. If only one bit is transferred per clock cycle in a serial link, it follows that either the serial bit clock has to be substantially faster than the parallel bus, or the link’s bandwidth will be significantlybelow that of the parallel bus. Bandwidth in a communication context refers to the capacity of the communications channel, often expressed either in bits-per-second (bps) or bytes-per-second (Bps). Serial links are available in a broad spectrum of bandwidths, from thousands of bits per second (kbps) to billions of bits per second (Gbps) and are stretching toward trillions of bits per second (Tbps)!
