Each memory chip of a memory module tests a total of N data bits from X memory blocks for efficient testing and outputs N/X test data bits from one of the memory blocks. A memory module includes a plurality of memory chips and a plurality of comparison units. Each comparison unit is disposed within a respective memory chip for testing a plurality of test data bits from a plurality of memory blocks. In addition, each comparison unit outputs test data bits from one of the memory blocks within the respective memory chip.