The System 7.5.5 Update is a set of system software enhancements that improves the reliability and performance of all Macintosh and Mac OS-compatible computers running system software version 7.5.3. The system 7.5.5 update also includes all the improvements delivered with 7.5.3 Revision 2. Therefore, it is not necessary to install System 7.5.3 Revision 2 before installing System 7.5.5 Update.
Apple
www.apple.com