A controller for a nonvolatile memory includes an encoder and a decoder. The memory includes memory cells that each store data using more than two levels. The encoder generates first data for storage in first memory cells. For first and second subsets of cells of the first memory cells, the first data is stored at first and second levels, respectively. Measurable values of the first subset of cells are characterized by a first probability density function having a first width. Measurable values of the second subset of cells are characterized by a second probability density function having a second width. The first width is greater than the second width. The encoder generates the first data such that a size of the first subset of cells is less than a size of the second subset of cells. The decoder decodes encoded data from the memory.