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Implementing MLC NAND Flash for Cost-Effective, High-Capacity Memory
91-SR-014-02-8L 11
Efficient Bad Block Handling
x2 technology handles bad blocks, which can be randomly present in flash media, by enabling
unaligned block access to two planes. Bad blocks are mapped individually on each plane, as shown
in Figure 4. Good units can therefore be aligned or unaligned, minimizing the effects of bad blocks
on the media. Without this capability, a bad block in one plane would cause a good block in the
second plane to be tagged as a bad block, making it unusable. This customized method of bad block
handling for two planes enhances data reliability without adversely affecting performance.
Bad Unit Good Unit
Good Unit
16-bit Data Bus
Bad Unit
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16-bit Data Bus
Flash Plane 2Flash Plane 1
Internal Bus
Good Unit Good UnitAligned Unit
Good Unit Good UnitAligned Unit
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Good Unit Good UnitAligned Unit
Good Unit Good UnitAligned Unit
Good Unit Good UnitAligned Unit
Figure 4: Unaligned Multiplane Bad Block Access