This graphic shows a horizontal series of blocks. The first 10 blocks are black. The next 3 are gray. The last 1 are white. The edge shared by the black and gray blocks is labeled "Low HWM." The edge shared by the gray and white blocks is labeled "HWM." The legend indicates that a white block is "Never Used, Unformatted." A gray block is "Unknown." A black block is "Used."