A cooperating data compressor, compressed data format, and data decompressor. The compressor compresses an input data block (HB) to a compressed data block having the format. The decompressor decompresses the compressed data block to restore the original data block. The compressor has a direct lookup table (DLT) of 2.sup.8.times.N entries, each indexable by N bytes at a current HB location and identifying a target HB location. The compressor determines whether a target string at the target HB location matches a current string at the current HB location. If they do not match, the compressor outputs a literal representing a datum at the current location. If they match, the compressor outputs a vector from the current location to the target string. Compression speed is maximized by the direct addressing of the DLT by the current N bytes in the HB. Decompression speed is maximized by state machine operation according to literal/vector indicators, special case string length codes, and special case offset codes in the compressed data format.