The algorithm used by the Unix compress command to reduce the size of files, e.g. for archival storage or transmission. LZW was designed by Terry Welch in 1984 for use in hardware for high-performance disk controllers. It is a variant of LZ78, one of the two Lempel-Ziv compression schemes. It maintains a table mapping input strings to their associated output codes. The table initially contains mappings for all possible strings of length one.
Input is taken one byte at a time to find the longest initial string present in the table.
The process repeats, starting from byte b. The number of bits in an output code, and hence the maximum number of entries in the table is usually fixed and once this limit is reached, no more entries are added. Time as measured by the right ascension of the hour circle that is currently at an observer's meridian . See also sidereal day . The sun has a systematic motion relative to nearby stars, the mean depending on the spectral type of the stars used for comparison.