Loss-less data compression/decompression especially useful in a limited resource environment such as a handheld portable video game system allows graphics and/or attribute data to be efficiently and quickly decompressed on an as-needed basis in real time response to interactive user inputs. A two-level run-length-encoding is used to encode redundant patterns and redundant symbols. A common sentinel field format encodes whether data following the field is non-redundant data, a symbol run, or a pattern run. Compression ratios of 60% for representative symbol-mapped video display graphics/attribute files can be achieved.