Data compression

A method comprising:

• transmitting, by a controller configured to control a nonvolatile memory device, a soft read command to the nonvolatile memory device;
• generating, by the nonvolatile memory device, soft-bit data in response to the soft read command;
• providing, by a control logic circuit of the nonvolatile memory device, a stage control signal to a compression circuit, to control compression by the compression circuit in a plurality of compression stages;
• generating, by the compression circuit, compressed soft-bit data by compressing the soft-bit data based on the stage control signal;
• and
• transmitting, by the nonvolatile memory device, the compressed soft-bit data to the controller,
• wherein the stage control signal controls whether compression in each of the plurality of compression stages is performed.

A storage device comprising:

• a nonvolatile memory device configured to store and read user data;
• and
• a controller configured to control the nonvolatile memory device,
• wherein the nonvolatile memory device includes:
• a memory cell array including a plurality of memory cells configured to store data bits corresponding to the user data,
• a plurality of compression circuits configured to compress soft-bit data sensed from the plurality of memory cells, and
• a control logic circuit configured to control the plurality of compression circuits, wherein the plurality of compression circuits include:
• a converting circuit configured to, based on a mapping table, convert the soft-bit data into input data comprising index codes and dummy codes,
• a first compression circuit configured to compress the input data at a first compression ratio, to obtain first output data,
• a second compression circuit configured to receive the first output data from the first compression circuit and to generate second output data by compressing the first output data at a second compression ratio,
• wherein the control logic circuit controls whether the first output data is provided to the second compression circuit based on a target compression ratio for the soft-bit data.