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Memory for disk arrays

If, for example, the amount is equal to four words (in binary record 100), you can write that number in binary form, will require three-level, it means that the size of contracts checklist is three words. Therefore, if you have four discs to store data, the need for an additional three-disc for storing control data. Similarly, if the seven disks for data (binary record 111) will need three disk storage control words. If the figures given by the eight discs (binary record 1000), the need to drive four-horse quiz information. Hamming code, forming the word checklist, based on the use of porazryadnoy operations "excluding " OR (XOR) (also used the name "disparity") - logs-agency unit gives XOR operation with the noncoincidence operands (0 and 1) and zero when they coincidence (0 and 0 or 1 and 1). The very word checklist, obtained by the algorithm Hemminga - is a result of inversion porazryadnoy exclusive OR operation rooms of the information bits words, the values of which are equal 1. To illustrate, consider the original 1101 floor. The first (001), third (011) and fourth (100) volume level is a unit of the word. It is therefore necessary to hold porazryadnuyu exclusive OR operation for 100 = 110. 011 these rooms bits: 001 The very same word checklist (Hamming code) is produced when porazryadnom invertirovanii the result, that is equal to 001. When a newly calculated data and code Hemminga compared with the source code. To compare the two codes used porazryadnaya "exclusive OR operation." If the result of comparison in all bits equal to zero, the reading is correct, otherwise its value is room mistakenly taken basic-level code. Let us, for example, the original floor well 1100000. Because the units are at the sixth (110) and seventh (111) positions checklist layer of equals 110.
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