Communication We divided the world s tech nological communication capacity into

Communication we divided the world s tech nological

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Communication. We divided the world s tech- nological communication capacity into two broad groups: One includes technological sys- tems that provide only unidirectional downstream capacity to diffuse information (referred to as broadcasting), and one provides bidirectional up- stream and downstream channels (telecommu- nication). The ongoing technological convergence between broadcasting and telecommunication is blurring this distinction, as exemplified by the case of digital television, which we counted as broadcasting even though it incorporates a small but existent upstream channel (such as video-on- demand). Fig. 4. World s technological effective capacity to telecommunicate information (table SA2) ( 16 ). Fig. 5. World s technological installed capacity to compute information on general-purpose computers, in MIPS (table SA3) ( 16 ). 1 APRIL 2011 VOL 332 SCIENCE 62 RESEARCH ARTICLES
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The inventories of Figs. 3 and 4 account for only those bits that are actually communicated. In the case of telecommunication, the sum of the effective usages of all users is quite similar to the total installed capacity (any difference represents an over- or future investment). This is because most backbone networks are shared and only used sporadically by an individual user. If all users demanded their promised bandwidth simul- taneously, the network would collapse. This is not the case for individual broadcast subscribers, who could continuously receive incoming infor- mation. To meaningfully compare the carrying capacities of each, we applied effective consump- tion rates to the installed capacity of broadcasting (calling it the effective capacity). This reduced the installed capacity by a stable factor (by 9 in 1986, 9.1 in 1993, 8.7 in 2000, and 8.4 in 2007), implying an average individual broadcast con- sumption of roughly 2 hours and 45 min per 24 hours. It did not notably change the relative distribution of the diverse technologies (Fig. 3). Figure 3 displays the capacity of six analog and five digital broadcast technologies, including newspapers and personal navigation devices [glob- al postioning system (GPS)]. In 1986, the world s technological receivers picked up around 432 exabytes of optimally compressed information, 715 optimally compressed exabytes in 1993, 1.2 optimally compressed zettabytes in 2000, and 1.9 optimally compressed zettabytes in 2007. Cable and satellite TV steadily gained importance, but analog, over-the-air terrestrial television still dominated the evolutionary trajectory. Digital satellite television led the pack into the digital age, receiving 50% of all digital broadcast signals in 2007. Only a quarter of all broadcasting in- formation was in digital format in 2007. The share of radio declined gradually from 7.2% in 1986 to 2.2% in 2007. Figure 4 presents effective capacity of the three most common bidirectional analog tele- communication technologies and their four most prominent digital heirs. The 281 petabytes of op- timally compressed information from 1986 were overwhelmingly dominated by fixed line teleph- ony, whereas postal letters contributed only 0.34%.
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