and product specifications from equipment producers We filled in occasional

And product specifications from equipment producers

This preview shows page 3 - 5 out of 7 pages.

and product specifications from equipment producers. We filled in occasional blanks with either linear or exponential interpolations, de- pending on the nature of the process in question. Frequently, we compared diverse sources for the same phenomena and strove for reasonable middle grounds in case of contradictions. In cases in which specific country data were not available, we aimed for a globally balanced outlook by creating at least two international profiles, one for the developed member countries of the Organ- isation for Economic Co-operation and Develop- ment (OECD) and another one for the rest of the world. Information, not hardware with redundant data. 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 of information that is handled by this hardware. Therefore, we converted the data contained in storage and communication hardware capaci- ty into informational bits by normalizing on compression rates. This addresses the fact that information sources have different degrees of redundancy. The redundancy (or predictability) of the source is primarily determined by the con- tent in question, such as text, images, audio, or video ( 29 , 30 ). Considering the kind of content, we measured information as if all redundancy were removed with the most efficient compres- sion algorithms available in 2007 (we call this level of compression optimally compressed ). Shannon ( 29 ) showed that the uttermost com- pression of information approximates the entropy of the source, which unambiguously quantifies the 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 of information that reduces uncertainty by half (re- garding a given probability space, such as letters from an alphabet or pixels from a color scale). This definition is independent of the specific task Fig. 2. World s technological installed capacity to store information (table SA1) ( 16 ). Fig. 3. World s technological effective capacity to broadcast information in optimally compressed megabytes MB per year, for 1986, 1993, 2000, and 2007; semi-logarithmic plot (table SA2) ( 16 ). SCIENCE VOL 332 1 APRIL 2011 61 RESEARCH ARTICLES
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or content. For example, after normalization on optimally compressed bits we can say things like a 6-cm 2 newspaper image is worth a 1000 words because both require the same average number of binary yes/no decisions to resolve the same amount of uncertainty. Normalization on compression rates is essen- tial for comparing the informational performance of analog and digital technologies. It is also in- dispensable for obtaining meaningful time series of digital technologies because more efficient compression algorithms enable us to handle more information with the same amount of hardware.
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