Abstract: A header analyzing unit extracts a header area and each table unit area in each of an old and a new executable files, and calls a difference extracting unit for each area. A segment data associating unit associates a segment data in the old executable file with a corresponding segment data in the new executable file, and calls the difference extracting unit for the associated areas. A resource associating unit associates a resource data in the old executable file with a corresponding resource data in the new executable file, and calls the difference extracting unit for the associated areas. The difference extracting unit extracts the differences in byte units between the new and the old executable files from start to end in a specified area, and saves the differences in an update file.

Abstract: A repeater for packet data optical communication between terminal devices includes a first section and a second section. The first section includes a first device for receiving a first optical signal transmitted from a terminal device and for converting the first optical signal into a first electric signal, a second device for frequency-converting the first electric signal to a second electric signal, and a third device for converting the second electric signal into a second optical signal and for transmitting the second optical signal. The second section includes a fourth device for receiving a third optical signal and for converting the third optical signal into a third electric signal, a fifth device for frequency-converting the third electric signal to a fourth electric signal, and a sixth device for converting the fourth electric signal into a fourth optical signal and for transmitting the fourth optical signal to a terminal device.