Method of correcting errors in binary coded words

Claim 1

A method of correcting errors in binary coded words organized in a word block consisting of a plurality of data words and a plurality of error check words and consisting of a plurality of subblocks which can be selectively grouped on the basis of one of three different criteria to form one of three different sets of subblocks which consist of first, second and third sets of subblocks wherein, if at least two of the data words and error check words in said word block are included in one of said first, second and third subblocks, said at least two of the data words and error check words could not be concurrently included within each of the other subblocks, comprising generating a first error correction code on the basis of each of the subblocks in said first set of subblocks, a second error correction code on the basis of each of the subblocks in said second set of subblocks, and an error detection code on the basis of each of the subblocks in said third set of subblocks, adding a binary coded flag to each of said plurality of data words and said plurality of error check words, said flag being indicative of the presence or absence of an error within the word to which the flag is added, detecting errors within each of said third set of subblocks on the basis of each of said error detection codes, correcting errors within each of said first set of subblocks on the basis of said first error correction code with reference to the flags respectively added to the words in each of the subblocks and correcting errors within each of said second set of subblocks on the basis of said second error correction code with reference to the flags respectively added to the words in each of the subblocks, altering the flag of any of the data and error check words in each of said first set of subblocks each time the correction of errors within each of said first set of subblocks is complete and altering the flag of any of the data and error check words in each of said second set of subblocks each time the correction of errors within each of said second set of subblocks is complete thereafter so that, each time the flag is altered, the flag is indicative of the absence of an error if a word being checked for an error is unlikely to contain an error and indicative of the presence of an error if the word being checked for an error is likely to contain an error or is likely to fail to be detected to be in error, altering the flag of any of the data and error check words if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is executed immediately upon correction of errors, and maintaining the flag of any of the data and error check words so that the flag maintained coincides with the flag added to the word being checked for an error before the word was corrected if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is not executed immediately upon correction of errors, characterized in that correction of errors is effected a plurality of times for the data and error check words in a subblock on the basis of at least one of the first error correction code and the second error correction code and in that the manner of altering the flag of any of the data and error check words in each of said first set of subblocks or in each of said second set of subblocks and the manner of correcting errors within each of said third set of subblocks are varied depending upon the numbers of times the correction of errors is repeated.

Claim 2

A method of correcting errors in binary coded words organized in a word block consisting of a plurality of data words and a plurality of error check words and consisting of a plurality of subblocks which can be selectively grouped on the basis of one of three different criteria to form one of three different sets of subblocks which consist of first, second and third sets of subblocks wherein, if at least two of the data words and error check words in said word block are included in one of said first, second and third subblocks, said at least two of the data words and error check words could not be concurrently included within each of the other subblocks, comprising generating a first error correction code on the basis of each of the subblocks in said first set of subblocks, a second error correction code on the basis of each of the subblocks in said second set of subblocks, and an error detection code on the basis of each of the subblocks in said third set of subblocks, adding a binary coded flag to each of said plurality of data words and said plurality of error check words, said flag being indicative of the presence or absence of an error within the word to which the flag is added, detecting errors within each of said third set of subblocks on the basis of each of said error detection codes, correcting errors within each of said first set of subblocks on the basis of said first error correction code with reference to the flags respectively added to the words in each of the subblocks and correcting errors within each of said second set of subblocks on the basis of said second error correction code with reference to the flags respectively added to the words in each of the subblocks, altering the flag of any of the data and error check words in each of said first set of subblocks each time the correction of errors within each of said first set of subblocks is complete and altering the flag of any of the data and error check words in each of said second set of subblocks each time the correction of errors within each of said second set of subblocks is complete thereafter so that, each time the flag is altered, the flag is indicative of the absence of an error if a word being checked for an error is unlikely to contain an error and indicative of the presence of an error if the word being checked for an error is likely to contain an error or is likely to fail to be detected to be in error, altering the flag of any of the data and error check words if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is executed immediately upon correction of errors, and maintaining the flag of any of the data and error check words so that the flag maintained coincides with the flag added to the word being checked for an error before the word was corrected if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is not executed immediately upon correction of errors, characterized in that correction of errors is effected a plurality of times for the data and error check words in a subblock on the basis of at least one of the first error correction code and the second error correction code and in that the manner of altering the flag of any of the data and error check words in each of said first set of subblocks or in each of said second set of subblocks and the manner of correcting errors within each of said third set of subblocks are varied depending upon the numbers of times the correction of errors is repeated.

Claim 8

A method of correcting errors in binary coded words organized in a word block consisting of a plurality of data words and a plurality of error check words and consisting of a plurality of subblocks which can be selectively grouped on the basis of one of three different criteria to form one of three different sets of subblocks which consist of first, second and third sets of subblocks wherein, if at least two of the data words and error check words in said word block are included in one of said first, second and third subblocks, said at least two of the data words and error check words could not be concurrently included within each of the other subblocks, comprising generating a first error correction code on the basis of each of the subblocks in said first set of subblocks, a second error correction code on the basis of each of the subblocks in said second set of subblocks, and an error detection code on the basis of each of the subblocks in said third set of subblocks, adding a binary coded flag to each of said plurality of data words and said plurality of error check words, said flag being indicative of the presence or absence of an error within the word to which the flag is added, detecting errors within each of said third set of subblocks on the basis of said error detection codes, correcting errors within each of said first set of subblocks on the basis of said first error correction code with reference to the flags respectively added to the words in each of the subblocks and correcting errors within each of said second set of subblocks on the basis of said second error correction code with reference to the flags respectively added to the words in each of the subblocks, altering the flag of any of the data and error check words in each of said first set of subblocks each time the correction of errors within each of said first set of subblocks is complete and altering the flag of any of the data and error check words in each of said second set of subblocks each time the correction of errors within each of said second set of subblocks is complete thereafter so that, each time the flag is altered, the flag is indicative of the absence of an error if a word being checked for an error is unlikely to contain an error and indicative of the presence of an error if the word being checked for an error is likely to contain an error or is likely to fail to be detected to be in error, altering the flag of any of the data and error check words if the flag has remained unaltered after correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is executed immediately upon correction of errors, and maintaining the flag of any of the data and error check words so that the flag maintained coincides with the flag added to the word being checked for an error before the word was corrected if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is not executed immediately upon correction of errors, wherein each of said first error correction code and said second error correction code is such that is capable of correcting up to two words in each of said first set of subblocks and up to two words in each of said second set of subblocks, respectively, if the location of the words in error in a subblock being checked for an error is known and correcting a single word in each of said first set of subblocks and a single word in each of said second set of subblocks, respectively, if the location of the words in error in the subblock being checked for an error is unknown, the word at the error location determined on the basis of said first error correction code or said second error correction code being corrected if the subblock including the erred word to be corrected contains therein one word erred with an incorrect flag added thereto before the error in the word at said error location was corrected and if additionally said error location is found to correspond to any one of the words in the subblock being checked for an error, the flags of all the words in any of said first set of subblocks or any of said second set of subblocks being altered to be indicative of the absence of errors in the words being checked for errors if the subblock including the erred word to be corrected contains therein one word erred with an incorrect flag added thereto before the error in the word was corrected and if additionally either it is found on the basis of said first error correction code or said second error correction code that there is no erred word in the subblock being checked for an error or the flag of the word at the error location determined on the basis of said first error correction code or said second error correction code is indicative of the presence of an error in the word, and the flags of all the words in any of said first set of subblocks or any of said second set of subblocks being altered to be indicative of the presence of errors in the words being checked for errors if the subblock including the erred word to be corrected contains therein one word erred with an incorrect flag added thereto before the error in the word was corrected and if additionally the word at the error location determined on the basis of said first error correction code or said second error correction code is found to correspond to none of the words in the subblock being checked for an error.

Claim 9

A method of correcting errors in binary coded words organized in a word block consisting of a plurality of data words and a plurality of error check words and consisting of a plurality of subblocks which can be selectively grouped on the basis of one of three different criteria to form one of three different sets of subblocks which consist of first, second and third sets of subblocks wherein, if at least two of the data words and error check words in said word block are included in one of said first, second and third subblocks, said at least two of the data words and error check words could not be concurrently included within each of the other subblocks, comprising generating a first error correction code on the basis of each of the subblocks in said first set of subblocks, a second error correction code on the basis of each of the subblocks in said second set of subblocks, and an error detection code on the basis of each of the subblocks in said third set of subblocks, adding a binary coded flag to each of said plurality of data words and said plurality of error check words, said flag being indicative of the presence or absence of an error within the word to which the flag is added, detecting errors within each of said third set of subblocks on the basis of said error detection codes, correcting errors within each of said first set of subblocks on the basis of said first error correction code with reference to the flags respectively added to the words in each of the subblocks and correcting errors within each of said second set of subblocks on the basis of said second error correction code with reference to the flags respectively added to the words in each of the subblocks, altering the flag of any of the data and error check words in each of said first set of subblocks each time the correction of errors within each of said first set of subblocks is complete and altering the flag of any of the data and error check words in each of said second set of subblocks each time the correction of errors within each of said second set of subblocks is complete thereafter so that, each time the flag is altered, the flag is indicative of the absence of an error if a word being checked for an error is unlikely to contain an error and indicative of the presence of an error if the word being checked for an error is likely to contain an error or is likely to fail to be detected to be in error, altering the flag of any of the data and error check words if the flag has remained unaltered after correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is executed immediately upon correction of errors, and maintaining the flag of any of the data and error check words so that the flag maintained coincides with the flag added to the word being checked for an error before the word was corrected if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is not executed immediately upon correction of errors, wherein each of said first error correction code and said second error correction code is such that is capable of correcting up to two words in each of said first set of subblocks and up to two words in each of said second set of subblocks, respectively, if the location of the words in error in a subblock being checked for an error is known and correcting a single word in each of said first set of subblocks and a single word in each of said second set of subblocks, respectively, if the location of the words in error in the subblock being checked for an error is unknown, the word at the error location determined on the basis of said first error correction code or said second error correction code being corrected if the subblock including the erred word to be corrected contains therein one word erred with an incorrect flag added thereto before the error in the word at said error location was corrected and if additionally said error location is found to correspond to any one of the words in the subblock being checked for an error, the flags of all the words in any of said first set of subblocks or any of said second set of subblocks being altered to be indicative of the absence of errors in the words being checked for errors if the subblock including the erred word to be corrected contains therein one word erred with an incorrect flag added thereto before the error in the word was corrected and if additionally either it is found on the basis of said first error correction code or said second error correction code that there is no erred word in the subblock being checked for an error or the flag of the word at the error location determined on the basis of said first error correction code or said second error correction code is indicative of the presence of an error in the word, and the flags of all the words in any of said first set of subblocks or any of said second set of subblocks being altered to be indicative of the presence of errors in the words being checked for errors if the subblock including the erred word to be corrected contains therein one word erred with an incorrect flag added thereto before the error in the word was corrected and if additionally the word at the error location determined on the basis of said first error correction code or said second error correction code is found to correspond to none of the words in the subblock being checked for an error.

Claim 10

A method of correcting errors in binary coded words organized in a word block consisting of a plurality of data words and a plurality of error check words and consisting of a plurality of subblocks which can be selectively grouped on the basis of one of three different criteria to form one of three different sets of subblocks which consist of first, second and third sets of subblocks wherein, if at least two of the data words and error check words in said word block are included in one of said first, second and third subblocks, said at least two of the data words and error check words could not be concurrently included within each of the other subblocks, comprising generating a first error correction code on the basis of each of the subblock in said first set of subblocks, a seoond error correction code on the basis of each of the subblocks in said second set of subblocks, and an error detection code on the basis of each of the subblocks in said third set of subblocks, adding a binary coded flag to each of said plurality of data words and said plurality of error check words, said flag being being indicative of the presence or absence of an error within the word to which the flag is added, detecting errors within each of said third set of subblocks on the basis of each of said error detection codes, correcting errors within each of said first set of subblocks on the basis of said first error correction code with reference to the flags respectively added to the words in each of the subblocks and correcting errors within each of said second set of subblocks on the basis of said second error correction code with reference to the flags respectively added to the words in each of the subblocks, altering the flag of any of the data and error check words in each of said first set of subblocks each time the correction of errors within each of said first set of subblocks is complete and altering the flag of any of the data and error check words in each of said second set of subblocks each time the correction of errors within each of said second set of subblocks is complete thereafter so that, each time the flag is altered, the flag is indicative of the absence of an error if a word being checked for an error is unlikely to contain an error and indicative of the presence of an error if the word being checked for an error is likely to contain an error or is likely to fail to be detected to be in error, altering the flag of any of the data and error check words depending upon the result of the detection if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is executed immediately upon correction of errors, and maintaining the flag of any of the data and error check words so that the flag altered or maintained coincides with the flag added to the word being checked for an error before the word was corrected if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is not executed immediately upon correction of errors, wherein each of said first error correction code and said second error correction code is such that is capable of correcting up to two words in each of said first set of subblocks and up to two words in each of said second set of subblocks, respectively, if the location of the words in error in a subblock being checked for an error is known and correcting a single word in each of said first set of subblocks and a single word in each of said second set of subblocks, respectively, if the location of the words in error in a subblock being checked for an error is unknown, the error in a word indicated to be in error by the flag added thereto in any of said first set of subblocks being corrected on the basis of said first error correction code and the error in a word indicated to be in error by the flag added thereto in any of said second set of subblocks being corrected on the basis of said second error correction code if the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of the first set of subblocks being altered to be indicative of the absence of errors in the subblock being checked for an error if it is found on the basis of said first error correction code that there is no erred word in the subblock being checked for an error and the flags of all the data and error check words in any of the second set of subblocks being altered to be indicative of the absence of errors in the subblock being checked for an error if it is found on the basis of said second error correction code that there is no erred word in the subblock being checked for an error, if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of the first set of subblocks being maintained or altered to be identical in the subblock being checked for an error if the flag of the word at the error location determined on the basis of said first error correction code is indicative of the presence of an error in the word and the flags of all the data and error check words in any of the second set of subblocks being maintained or altered to be identical in the subblock being checked for an error if the flag of the word at the error location determined on the basis of said second error correction code is indicative of the presence of an error in the word, and if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of said first set of subblocks or any of said second set of subblocks being altered to be indicative of the presence of errors in the subblock being checked for an error if the error location determined on the basis of said first error correction code or said second error correction code is not the location where the flag of the word is indicative of the presence of an error.

Claim 11

A method of correcting errors in binary coded words organized in a word block consisting of a plurality of data words and a plurality of error check words and consisting of a plurality of subblocks which can be selectively grouped on the basis of one of three different criteria to form one of three different sets of subblocks which consist of first, second and third sets of subblocks wherein, if at least two of the data words and error check words in said word block are included in one of said first, second and third subblocks, said at least two of the data words and error check words could not be concurrently included within each of the other subblocks, comprising generating a first error correction code on the basis of each of the subblock in said first set of subblocks, a seoond error correction code on the basis of each of the subblocks in said second set of subblocks, and an error detection code on the basis of each of the subblocks in said third set of subblocks, adding a binary coded flag to each of said plurality of data words and said plurality of error check words, said flag being being indicative of the presence or absence of an error within the word to which the flag is added, detecting errors within each of said third set of subblocks on the basis of each of said error detection codes, correcting errors within each of said first set of subblocks on the basis of said first error correction code with reference to the flags respectively added to the words in each of the subblocks and correcting errors within each of said second set of subblocks on the basis of said second error correction code with reference to the flags respectively added to the words in each of the subblocks, altering the flag of any of the data and error check words in each of said first set of subblocks each time the correction of errors within each of said first set of subblocks is complete and altering the flag of any of the data and error check words in each of said second set of subblocks each time the correction of errors within each of said second set of subblocks is complete thereafter so that, each time the flag is altered, the flag is indicative of the absence of an error if a word being checked for an error is unlikely to contain an error and indicative of the presence of an error if the word being checked for an error is likely to contain an error or is likely to fail to be detected to be in error, altering the flag of any of the data and error check words depending upon the result of the detection if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is executed immediately upon correction of errors, and maintaining the flag of any of the data and error check words so that the flag altered or maintained coincides with the flag added to the word being checked for an error before the word was corrected if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is not executed immediately upon correction of errors, wherein each of said first error correction code and said second error correction code is such that is capable of correcting up to two words in each of said first set of subblocks and up to two words in each of said second set of subblocks, respectively, if the location of the words in error in a subblock being checked for an error is known and correcting a single word in each of said first set of subblocks and a single word in each of said second set of subblocks, respectively, if the location of the words in error in a subblock being checked for an error is unknown, the error in a word indicated to be in error by the flag added thereto in any of said first set of subblocks being corrected on the basis of said first error correction code and the error in a word indicated to be in error by the flag added thereto in any of said second set of subblocks being corrected on the basis of said second error correction code if the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of the first set of subblocks being altered to be indicative of the absence of errors in the subblock being checked for an error if it is found on the basis of said first error correction code that there is no erred word in the subblock being checked for an error and the flags of all the data and error check words in any of the second set of subblocks being altered to be indicative of the absence of errors in the subblock being checked for an error if it is found on the basis of said second error correction code that there is no erred word in the subblock being checked for an error, if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of the first set of subblocks being maintained or altered to be identical in the subblock being checked for an error if the flag of the word at the error location determined on the basis of said first error correction code is indicative of the presence of an error in the word and the flags of all the data and error check words in any of the second set of subblocks being maintained or altered to be identical in the subblock being checked for an error if the flag of the word at the error location determined on the basis of said second error correction code is indicative of the presence of an error in the word, and if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of said first set of subblocks or any of said second set of subblocks being altered to be indicative of the presence of errors in the subblock being checked for an error if the error location determined on the basis of said first error correction code or said second error correction code is not the location where the flag of the word is indicative of the presence of an error.

Claim 12

A method of correcting errors in binary coded words orgainzed in a word block consisting of a plurality of data words and a plurality of error check words and consisting of a plurality of subblocks which can be selectively grouped on the basis of one of three different criteria to form one of three different sets of subblocks which consist of first, second and third sets of subblocks wherein, if at least two of the data words and error check words in said word block are included in one of said first, second and third subblocks, said at least two of the data words and error check words could not be concurrently included within each of the other subblocks, comprising generating a first error correction code on the basis of each of the subblocks in said first set of subblocks, a second error correction code on the basis of each of the subblocks in said second set of subblocks, and an error detection code on the basis of each of the subblocks in said third set of subblocks, adding a binary coded flag to each of said plurality of data words and said plurality of error check words, said flag being indicative of the presence or absence of an error within the word to which the flag is added, detecting errors within each of said third set of subblocks on the basis of each of said error detection codes, correcting errors within each of said first set of subblocks on the basis of said first error correction code with reference to the flags respectively added to the words in each of the subblocks and correcting errors within each of said second set of subblocks on the basis of said second error correction code with reference to the flags respectively added to the words in each of the subblocks, altering the flag of any of the data and error check words in each of said first set of subblocks each time the correction of errors within each of said first set of subblocks is complete and altering the flag of any of the data and error check words in each of said second set of subblocks each time the correction of errors within each of said second set of subblocks is complete thereafter so that, each time the flag is altered, the flag is indicative of the absence of an error if a word being checked for an error is unlikely to contain an error and indicative of the presence of an error if the word being checked for an error is likely to contain an error or is likely to fail to be detected to be in error, altering the flag of any of the data and error check words depending upon the result of the detection if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is executed immediately upon correction of errors, and maintaining the flag of any of the data and error check words so that the flag altered or maintained coincides with the flag added to the word being checked for an error before the word was corrected if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is not executed immediately upon correction of errors, wherein each of said first error correction code and said second error correction code is such that is capable of correcting up to two words in each of said first set of subblocks and up to two words in each of said second set of subblocks, respectively, if the location of the words in error in a subblock being checked for an error is known and correcting a single word in each of said first set of subblocks and a single word in each of said second set of subblocks, respectively, if the location of the words in error in the subblock being checked for an error is unknown, the error in a word indicated to be in error by the flag added thereto in any of said first set of subblocks being corrected on the basis of said first error correction code and the error in a word indicated to be in error by the flag added thereto in any of said second set of subblocks being corrected on the basis of said second error correction code if the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of the first set of subblocks being altered to be indicative of the absence of errors in the subblock being checked for an error if it is found on the basis of said first error correction code that there is no erred word in the subblock being checked for an error and the flags of all the data and error check words in any of the second set of subblocks being altered to be indicative of the absence of errors in the subblock being checked for an error if it is found on the basis of said second error correction code that there is no erred word in the subblock being checked for an error, if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of said first set of subblocks or any of said second set of subblocks being maintained or altered to be indicative of the absence of errors in the subblock being checked for an error if the flag of the word at the error location determined on the basis of said first error correction code is indicative of the presence of an error in the word and the flags of all the data and error check words in any of the second set of subblocks being maintained or altered to be identical in the subblock being checked for an error if the flag of the word at the error location determined on the basis of said second error correction code is indicative of the presence of an error in the word, and if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of only the two words corrected in any of said first set of subblocks being altered to be indicative of the presence of errors in the subblock being checked for an error if the error location determined on the basis of said first error correction code or said second error correction code is not the location where the flag of the word is indicative of the presence of an error.

Claim 13

A method of correcting errors in binary coded words orgainzed in a word block consisting of a plurality of data words and a plurality of error check words and consisting of a plurality of subblocks which can be selectively grouped on the basis of one of three different criteria to form one of three different sets of subblocks which consist of first, second and third sets of subblocks wherein, if at least two of the data words and error check words in said word block are included in one of said first, second and third subblocks, said at least two of the data words and error check words could not be concurrently included within each of the other subblocks, comprising generating a first error correction code on the basis of each of the subblocks in said first set of subblocks, a second error correction code on the basis of each of the subblocks in said second set of subblocks, and an error detection code on the basis of each of the subblocks in said third set of subblocks, adding a binary coded flag to each of said plurality of data words and said plurality of error check words, said flag being indicative of the presence or absence of an error within the word to which the flag is added, detecting errors within each of said third set of subblocks on the basis of each of said error detection codes, correcting errors within each of said first set of subblocks on the basis of said first error correction code with reference to the flags respectively added to the words in each of the subblocks and correcting errors within each of said second set of subblocks on the basis of said second error correction code with reference to the flags respectively added to the words in each of the subblocks, altering the flag of any of the data and error check words in each of said first set of subblocks each time the correction of errors within each of said first set of subblocks is complete and altering the flag of any of the data and error check words in each of said second set of subblocks each time the correction of errors within each of said second set of subblocks is complete thereafter so that, each time the flag is altered, the flag is indicative of the absence of an error if a word being checked for an error is unlikely to contain an error and indicative of the presence of an error if the word being checked for an error is likely to contain an error or is likely to fail to be detected to be in error, altering the flag of any of the data and error check words depending upon the result of the detection if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is executed immediately upon correction of errors, and maintaining the flag of any of the data and error check words so that the flag altered or maintained coincides with the flag added to the word being checked for an error before the word was corrected if the flag has remained unaltered after the correction of errors on the basis of said first error correction code or on the basis of said second error correction code and if additionally the detection of errors on the basis of said error detection code is not executed immediately upon correction of errors, wherein each of said first error correction code and said second error correction code is such that is capable of correcting up to two words in each of said first set of subblocks and up to two words in each of said second set of subblocks, respectively, if the location of the words in error in a subblock being checked for an error is known and correcting a single word in each of said first set of subblocks and a single word in each of said second set of subblocks, respectively, if the location of the words in error in the subblock being checked for an error is unknown, the error in a word indicated to be in error by the flag added thereto in any of said first set of subblocks being corrected on the basis of said first error correction code and the error in a word indicated to be in error by the flag added thereto in any of said second set of subblocks being corrected on the basis of said second error correction code if the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of the first set of subblocks being altered to be indicative of the absence of errors in the subblock being checked for an error if it is found on the basis of said first error correction code that there is no erred word in the subblock being checked for an error and the flags of all the data and error check words in any of the second set of subblocks being altered to be indicative of the absence of errors in the subblock being checked for an error if it is found on the basis of said second error correction code that there is no erred word in the subblock being checked for an error, if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of all the data and error check words in any of said first set of subblocks or any of said second set of subblocks being maintained or altered to be indicative of the absence of errors in the subblock being checked for an error if the flag of the word at the error location determined on the basis of said first error correction code is indicative of the presence of an error in the word and the flags of all the data and error check words in any of the second set of subblocks being maintained or altered to be identical in the subblock being checked for an error if the flag of the word at the error location determined on the basis of said second error correction code is indicative of the presence of an error in the word, and if also the subblock including the erred word to be corrected contains therein two words erred with incorrect flags added thereto before the error in said word indicated to be in error was corrected, the flags of only the two words corrected in any of said first set of subblocks being altered to be indicative of the presence of errors in the subblock being checked for an error if the error location determined on the basis of said first error correction code or said second error correction code is not the location where the flag of the word is indicative of the presence of an error.