Module Module 2 locule 3 FIGURE 93.1 Fault masking using triple modular redundancy (tmr) Spare Module 1 Fault Detection Reconfiguration Unit FIGURE 93.2 General concept of standby sparing. The final form of hardware redundancy is the hybrid approach. Hybrid techniques combine the attractive features of both the passive and active approaches. Fault masking is used in hybrid systems to prevent erroneous results from being generated. Fault detection, fault location, and fault recovery are also used in the hybrid approaches to improve fault tolerance by removing faulty hardware and replacing it with spares. Providing spares is one form of providing redundancy in a system. Hybrid methods are most often used in the critical computation applications where fault masking is required to prevent momentary errors, and high reliability must be achieved. The basic concept of the hybrid approach is illustrated in Fig. 93.3 93.3 Information Redundancy Another approach to fault tolerance is to employ redundancy of information. Information redundancy is simply the addition of redundant information to data to allow fault detection, fault masking, or possibly fault tolerance Good examples of information redundancy are error detecting and error correcting codes, formed by the addition of redundant information to data words or by the mapping of data words into new representation containing redundant information [Lin and Costello, 1983] In general, a code is a means of representing information, or data, using a well-defined set of rules. A code word is a collection of symbols, often called digits if the symbols are numbers, used to represent a particular piece of data based upon a specified code. a binary code is one in which the symbols forming each code word onsist of only the digits 0 and 1. A code word is said to be valid if the code word adheres to all of the rules that define the code: otherwise the code word is said to be invalid. e 2000 by CRC Press LLC© 2000 by CRC Press LLC The final form of hardware redundancy is the hybrid approach. Hybrid techniques combine the attractive features of both the passive and active approaches. Fault masking is used in hybrid systems to prevent erroneous results from being generated. Fault detection, fault location, and fault recovery are also used in the hybrid approaches to improve fault tolerance by removing faulty hardware and replacing it with spares. Providing spares is one form of providing redundancy in a system. Hybrid methods are most often used in the critical￾computation applications where fault masking is required to prevent momentary errors, and high reliability must be achieved. The basic concept of the hybrid approach is illustrated in Fig. 93.3. 93.3 Information Redundancy Another approach to fault tolerance is to employ redundancy of information. Information redundancy is simply the addition of redundant information to data to allow fault detection, fault masking, or possibly fault tolerance. Good examples of information redundancy are error detecting and error correcting codes, formed by the addition of redundant information to data words or by the mapping of data words into new representations containing redundant information [Lin and Costello, 1983]. In general, a code is a means of representing information, or data, using a well-defined set of rules. A code word is a collection of symbols, often called digits if the symbols are numbers, used to represent a particular piece of data based upon a specified code. A binary code is one in which the symbols forming each code word consist of only the digits 0 and 1. A code word is said to be valid if the code word adheres to all of the rules that define the code; otherwise, the code word is said to be invalid. FIGURE 93.1 Fault masking using triple modular redundancy (TMR). FIGURE 93.2 General concept of standby sparing. Module 1 Module 2 Voter Output Module 3