and product specifications from equipmentproducers. We filled in occasional blanks witheither linear or exponential interpolations, de-pending on the nature of the process in question.Frequently, we compared diverse sources forthe same phenomena and strove for reasonablemiddle grounds in case of contradictions. In casesin which specific country data were not available,we aimed for a globally balanced outlook bycreating at least two international profiles, one forthe“developed”member countries of the Organ-isation for Economic Co-operation and Develop-ment (OECD) and another one for the rest ofthe world.Information, not hardware with redundantdata.Although the estimation of the global hard-ware capacity for information storage and com-munication is of interest for the ICT industry(14), we are more interested in the amount ofinformation that is handled by this hardware.Therefore, we converted the data contained instorage and communication hardware capaci-ty into informational bits by normalizing oncompression rates. This addresses the fact thatinformation sources have different degrees ofredundancy. The redundancy (or predictability)of the source is primarily determined by the con-tent in question, such as text, images, audio, orvideo (29,30). Considering the kind of content,we measured information as if all redundancywere removed with the most efficient compres-sion algorithms available in 2007 (we call thislevel of compression“optimally compressed”).Shannon (29) showed that the uttermost com-pression of information approximates the entropyof the source, which unambiguously quantifiesthe amount of information contained in the mes-sage. In an information theoretic sense (30), in-formation is defined as the opposite of uncertainty.Shannon (29) defined one bit as the amount ofinformation that reduces uncertainty by half (re-garding a given probability space, such as lettersfrom an alphabet or pixels from a color scale).This definition is independent of the specific taskFig. 2.World’s technological installed capacity to store information (table SA1) (16).Fig. 3.World’s technological effective capacity to broadcast information in optimally compressedmegabytes MB per year, for 1986, 1993, 2000, and 2007; semi-logarithmic plot (table SA2) (16).SCIENCEVOL 3321 APRIL 201161RESEARCH ARTICLES
or content. For example, after normalization onoptimally compressed bits we can say things like“a 6-cm2newspaper image is worth a 1000 words”because both require the same average numberof binary yes/no decisions to resolve the sameamount of uncertainty.Normalization on compression rates is essen-tial for comparing the informational performanceof analog and digital technologies. It is also in-dispensable for obtaining meaningful time seriesof digital technologies because more efficientcompression algorithms enable us to handle moreinformation with the same amount of hardware.
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Test, Data storage device, Computer data storage, Digital television, Exabytes