Mac OS 7.5.5, also known as System 7.5.5, is a three-disk set of system software enhancements that delivers improvements in stability and performance for Macs and Mac clones. This update is for all Macs running Mac OS 7.5.3, and will result in the system being updated to version 7.5.5. Mac OS 7.5.5 included Mac OS 7.5.3 Revision 2 already, making an installation of Revision 2 unnecessary. Mac OS 7.5.5 must be installed on Mac OS 7.5.3; System 7.5 - Mac OS 7.5.2 users needed to transit through Mac OS 7.5.3 first before arriving at Mac OS 7.5.5.