some general characteristics of the present invention will be described with respect to fig2 . this description will be followed by a detailed description of various embodiments of the present invention in connection with fig3 - 8 . as shown in fig2 , a semiconductor memory 70 is repaired in accordance with the present invention by replacing memory blocks 72 and 74 with respective redundant rows 76 and 78 . the position and dimensions ( i . e ., number of rows and columns spanned ) of the memory blocks 72 and 74 are adjustable so an optimum number of defective memory cells 80 may be repaired using a minimum number of redundant rows . as a result , the present invention provides a highly efficient device and method for repairing a semiconductor memory . also , the present invention provides such repair efficiency without the need for an excessive number of fuses which is characteristic of the rountree repair system previously discussed . as shown in fig3 , selection fuses 90 in a semiconductor memory 92 of the present invention may be programmed to output a block repair enable signal en and fuse signals f ( 0 : 2 ) to select circuitry 94 . when active , the block repair enable signal en enables a block repair within an array 96 of the semiconductor memory 92 using a selected redundant row within the semiconductor memory 92 . when inactive , the block repair enable signal en enables conventional row repair within the array 96 using the selected redundant row . when block repair is enabled within the array 96 , the status of the fuse signals f ( 0 : 2 ) determines the dimensions of the repaired block . together , the fuse signals f ( 0 : 2 ) and the block repair enable signal en may sometimes be referred to as a “ block repair configuration .” it will be understood by those of ordinary skill in the art that only one enable signal en and only one set of fuse signals f ( 0 : 2 ) are shown in fig3 for purposes of clarity . in fact , redundant rows ( e . g ., rrow 0 , rrow 1 , rrow 2 , etc .) typically each have their own enable signal ( i . e ., en 0 , en 1 , en 2 , etc .) and their own set of fuse signals ( i . e ., f 0 ( 0 : 2 ), f 1 ( 0 : 2 ), f 2 ( 0 : 2 ), etc .) so that block repair or conventional repair can be selected for each redundant row using its enable signal , and so the dimensions of the repair block can be determined for each redundant row using its fuse signals if block repair is selected . for the purposes of this disclosure , rows and columns may be interchanged ( i . e ., instead of a redundant row , a redundant column may be used ). although the present invention will be described with respect to a 64 kb memory , it will be understood by those of ordinary skill in the art that the invention is applicable to any size memory . additionally , for the purposes of this detailed description , rows and columns may be interchanged ( i . e ., instead of a redundant row , a redundant column may be used .) it will also be understood that the invention is applicable to a wide variety of semiconductor memories , including , for example , magnetic random access memory ( mram ), dynamic ram ( dram ), synchronous dram ( sdram ), double data rate sdram ( ddr sdram ), rambus ® dram ( rdram ®), extended data - out dram ( edo dram ), fast - page - mode dram ( fpm dram ), static random access memory ( sram ), syncburst ™ sram , zero bus turnaround ™ sram ( zbt ™ sram , quad data rate ™ sram ( qdr ™ sram ), ddr synchronous sram ( ddr sram ) and nonvolatile electrically block - erasable programmable read only memory ( flash ). further , it will be understood by those of ordinary skill in the art that any nonvolatile element ( e . g ., fuses , antifuses , or flash eeprom cells ) will work for purposes of the selection fuses 90 , as will be explained in more detail below with respect to fig4 a , 4 b , and 4 c . upon receiving the enable signal en and the fuse signals f ( 0 : 2 ), the select circuitry 94 outputs selection signals s ( 0 : 7 ) as shown in table 1 below . of course , it will be understood by one of ordinary skill in the art that although only one set of selection signals s ( 0 : 7 ) is discussed here , in fact each redundant row within the array 96 typically has an associated set of selection signals s ( 0 : 7 ). in response to the selection signals s ( 0 : 7 ), and upon receiving row address signals ra ( 0 : 7 ) during a memory operation , mux circuitry 100 outputs compare signals cmp ( 0 : 7 ) as shown in table 2 , below . thus , mux circuitry 100 passes the most significant bits of the row address ra ( 0 : 7 ) through in accordance with the selection signals s ( 0 : 7 ). as will be discussed below , this determines the “ height ” ( i . e ., the number of rows spanned ) of a repair block . thus , for example , with the selection signals s ( 0 : 7 ) all set to zero , the repair block has the height of a single row ( because all bits of the row address ra ( 0 : 7 ) are passed through as compare signals cmp ( 0 : 7 )). this only occurs when the repair block enable signal en is inactive , so that conventional row repair is enabled . if , instead , the selection signals s ( 0 : 7 ) are set to fifteen , for example , then the repair block is sixteen rows high ( because the four most significant bits of the row address ra ( 0 : 7 ) are passed through the mux circuitry 100 ). finally , if the selection signals s ( 0 : 7 ) are set to two - hundred fifty - five , for example , then the repair block is two - hundred fifty - six rows high ( i . e ., the height of an entire column ). alternatively , the enable signal en may be eliminated if one combination of fuse signals f ( 0 : 2 ) is used to decode the disable state ( i . e ., f ( 0 : 2 ) all unprogrammed can represent block repair disable ). then , one of the states of selection signals s ( 0 : 7 ) will not be available since there would only be seven remaining states of selection signals s ( 0 : 7 ) in the above example . a portion of the address of a defective memory cell within the array 96 is stored using bad address storage fuses 102 ( hereinafter “ fuses 102 ”) and is output by the fuses 102 as bad address ba ( 0 : 7 ). if , for example , conventional row repair is being used to repair the defective memory cell , then the fuses 102 are programmed to output a bad address ba ( 0 : 7 ) equivalent to the row address of the defective cell . if , instead , a repair block sixteen rows high , for example , is being used to repair the defective cell , then the fuses 102 are programmed so the four most significant bits of the bad address ( i . e ., ba 7 , ba 6 , ba 5 , and ba 4 ) match the four most significant bits of the row address of the defective cell , and so the four least significant bits of the bad address ( i . e ., ba 3 , ba 2 , ba 1 , and ba 0 ) match the four most significant bits of the column address of the defective cell ( for reasons that will be explained below ). finally , if the repair block used to repair the defective cell is an entire column within the array 96 , then none of the fuses 102 are programmed with bits from the row address of the defective memory cell . instead , the fuses 102 are programmed with the column address of the defective memory cell ( again , for reasons that will be explained below ). of course , it will be understood by one of ordinary skill in the art that each redundant row in the array 96 typically has its own associated bad address ba ( 0 : 7 ). only one is discussed here for purposes of clarity . also , it will be understood that the fuses 102 may comprise any nonvolatile element including , for example , fuses , antifuses , or flash eeprom cells , as will be discussed below with respect to fig4 a , 4 b , and 4 c . the compare signals cmp ( 0 : 7 ) also include the column address ca ( 0 : 7 ) as shown in table 2 . the compare circuitry 104 compares the compare signals cmp ( 0 : 7 ) to the bad address ba ( 0 : 7 ). if there is no match , the column address ca ( 0 : 7 ) is used to select a column of the array 96 and the row decoder 106 selects a row address . when a match occurs , a column is selected by a column decoder 110 in accordance with redundant decode signals dec ( 0 : 7 ) that are output by the mux circuitry 100 as shown in table 3 , below . the selection fuses 90 and the bad address storage fuses 102 of fig3 may comprise any nonvolatile elements including , for example , fuses 120 as shown in fig4 a , antifuses 122 as shown in fig4 b , and flash eeprom cells 124 as shown in fig4 c . as shown in fig5 , the select circuitry 94 of fig3 includes a nor gate 130 , inverters 132 , and nand gates 134 for implementing the operations of the select circuitry 94 as described above with respect to table 1 . of course , it will be understood by one of ordinary skill in the art that any device for selecting the height and width of a repair block will work for purposes of the present invention , and that such a device need not necessarily include the circuitry shown in fig5 or operate in accordance with table 1 . as shown in fig6 , the mux circuitry 100 includes a plurality of mux circuits 140 for implementing the operations of the mux circuitry 100 as described above with respect to tables 2 , 3 , and 4 . again , it should be understood that any device for routing the proper row and column addresses to the compare circuitry 104 ( see fig3 ) will work for purposes of the present invention , and that such a device need not necessarily operate in accordance with tables 2 and 3 . it should be noted that , as described thus far , the present invention only uses repair blocks that stay within “ logical ” boundaries of the array 96 of fig3 . in addition , a repair block that spans one quarter of the rows in the top half of the array 96 , for example , and one quarter of the rows in the bottom half can be implemented using an alternative embodiment described below . in this embodiment , repair blocks that cross logical boundaries within the array 96 of fig3 may be used . for example , a repair block that spans an odd number of rows in the top half of the array 96 and an even number of rows in the bottom half of the array 96 can be implemented using this embodiment . such an embodiment typically requires that additional bad address storage fuses 102 ( see fig3 ) be provided to store additional bits from the row and column addresses of a defective memory cell . these additional bits are typically necessary to identify a match when row and column addresses are received . such an embodiment also typically requires that the compare circuitry 104 ( see fig3 ) be constructed to perform the necessary logical operations to determine a match . this embodiment thus requires additional fuses or other nonvolatile elements , but provides greater flexibility in selecting the optimum location of repair blocks . in the specific example described , the row address most significant bit ( msb ) may be replaced with an xor function of the msb and the next lower row address term for the repair address match . likewise , logical combinations of column address terms may be used in place of single column address terms to “ shift ” or split the repair block in the column dimension . for example , replacing the column msb with an xand function of the two most significant column address bits will split the repair block and match upper and lower quarters of the column address space rather than upper or lower halves . as shown in fig7 , the semiconductor memory 92 of fig3 is fabricated on a semiconductor wafer 160 . it should be understood that the semiconductor memory 92 may also be fabricated on a wide variety of other semiconductor substrates including , for example , a silicon - on - insulator ( soi ) substrate , a silicon - on - glass ( sog ) substrate , and a silicon - on - sapphire ( sos ) substrate . as shown in fig8 , an electronic system 170 includes an input device 172 , an output device 174 , a processor device 176 , and a memory device 178 that incorporates the semiconductor memory 92 of fig3 . of course , it should be understood that the semiconductor memory 92 may also be incorporated into any one of the input device 172 , the output device 174 , and the processor device 176 . although the present invention has been described with reference to particular embodiments , the invention is not limited to these described embodiments . rather , the invention is limited only by the appended claims , which include within their scope all equivalent devices or methods that operate according to the principles of the invention as described herein .