DATA PROCESSOR

PROBLEM TO BE SOLVED: To fast and effectively compress even such data that are in short of regularity and have a small number of iterative patterns by preserving the base data, comparing the data fetched successively with the base data to take out each difference between both data and preserving these difference data. SOLUTION: When the processing is started, the base data 217 serving as the base of comparison and recovery are saved to a compressed data saving file 215 from a source data file 201. A difference data saving program 212 compares the data 217 with the current data 202 contained in the file 201 to extract the difference data 204, 205... 209 and monitors whether or not the sizes of these data 204 to 209 are larger than the least number of bytes of difference storage. If those sizes exceed the least number of bytes, the difference data 219 are stored in a difference data area 216 included in the file 215 together with the individual difference data information 218 on the addresses, etc., of the data 219.