Read 
|------------|------------|------------|------------|---|
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....|s 7680 bits |s 7680 bits |s 7680 bits |s 7680 bits |
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write
<<<<|s-------|----s-------|----s-------|----s-------|---|
|s-------|----s-------|----s-------|----s-------|---|
-----------------------------------------------------
|s 7680 bits |s 7680 bits |s 7680 bits |s 7680 bits |
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