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In computing, triple modular redundancy, sometimes called triple-mode redundancy,〔(David Ratter. "FPGAs on Mars" )〕 (TMR) is a fault-tolerant form of N-modular redundancy, in which three systems perform a process and that result is processed by a majority-voting system to produce a single output. If any one of the three systems fails, the other two systems can correct and mask the fault. The TMR concept can be applied to many forms of redundancy, such as software redundancy in the form of N-version programming, and is commonly found in fault-tolerant computer systems. Some ECC memory uses triple modular redundancy hardware (rather than the more common Hamming code), because triple modular redundancy hardware is faster than Hamming error correction software.〔(【引用サイトリンク】publisher=Tsinghua Space Center, Tsinghua University, Beijing ) 〕 Space satellite systems often use TMR,〔(【引用サイトリンク】title=Actel engineers use triple-module redundancy in new rad-hard FPGA )〕 〔(SEU Hardening of Field Programmable Gate Arrays (FPGAs) For Space Applications and Device Characterization )〕〔(FPGAs in Space )〕 although satellite RAM usually uses Hamming error correction.〔(Commercial Microelectronics Technologies for Applications in the Satellite Radiation Environment )〕 Some communication systems use N-modular redundancy as a simple form of forward error correction. For example, 5-modular redundancy communication systems (such as FlexRay) use the majority of 5 samples – if any 2 of the 5 results are erroneous, the other 3 results can correct and mask the fault. Modular redundancy is a basic concept, dating to antiquity, while the first use of TMR in a computer was the Czechoslovak computer SAPO, in the 1950s. ==Chronometers== To use triple modular redundancy, a ship must have at least three chronometers; with only two chronometers (dual modular redundancy), error detection is possible, but error correction is not. There is an old adage to this effect, stating: "Never go to sea with two chronometers; take one or three." Mainly this means that if two chronometers contradict, how do you know which one is correct? At one time this observation or rule was an expensive one as the cost of three sufficiently accurate chronometers was more than the cost of many types of smaller merchant vessels. Some vessels carried more than three chronometers – for example, the HMS Beagle carried 22 chronometers.〔 (【引用サイトリンク】title=Volume II: Proceedings of the Second Expedition )〕 In the modern era, ships at sea use GNSS navigation receivers (with GPS, GLONASS & WAAS etc support) -- mostly running with WAAS or ENGOS support so as to provide accurate time (and location). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「triple modular redundancy」の詳細全文を読む スポンサード リンク
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