Memory device and memory system

A memory system comprising:

• a memory device;
• and
• a controller configured to provide a soft read command and error rate information to the memory device, wherein the memory device includes
• logic configured to generate soft data including at least a major symbol and at least a minor symbol in response to the soft read command,
• a selector configured to select, based on the soft read command and the error rate information, any one of a plurality of compression tables each indicating relationships between source alphabets and corresponding code alphabets,
• a compressor configured to generate compressed data by encoding the source alphabets detected from the soft data into the corresponding code alphabets according to the selected compression table, and
• provide the compressed data to the controller,
• wherein a source alphabet is not a prefix of another source alphabet within each of the plurality of compression tables,
• wherein a major source alphabet is the most likely to occur and has the longest length among the source alphabets within each of the plurality of compression tables, and
• wherein the code alphabet corresponding to the major source alphabet has the smallest length among the code alphabets within each of the plurality of compression tables.

A data system comprising:

• a memory device including a compressor configured to compress an original sequence including at least first and second symbols by referring to a table;
• and
• a controller including a decompressor configured to recover the original sequence from the compressed sequence by referring to the table,
• wherein the controller provides a soft read command and error rate information to the memory device,
• wherein the table includes original alphabets of different values and corresponding compressed alphabets of different values, the alphabets being defined according to a Huffman coding scheme,
• wherein each of the original alphabets of various lengths ends with one between the first and second symbols and a remaining part of the original alphabet is configured by repetitions of the first symbol, and
• wherein the compressed alphabet corresponding to the original alphabet ending with the first symbol is shorter than other compressed alphabets having the same length.