Two stage run and string data compressor providing doubly compressed output

A data compression/decompression system employs two stages of data compression. Information and/or character data is first formatted into M-bit width digital data characteristics for input to the first stage of the data compression system which comprises an expanding run length encoder having N-bit width output character where N>M and the number of M-bit width characters is greater than the number of N-bit width characters. The output of the expanding run length encoder is applied directly to a compatible adaptive string matching second stage data compression encoder of the type which is not degraded or affected by the input. When the input data stream to the two stage system is not of a known format or provided with leader or header bit character width information, a bit analyzer and a chopper are provided in a data stream to prepare the data stream in a bit character width format which matches the input of the expanding run length encoder.