system 7.5.5 included significant performance improvements for virtual memory and memory management on powerpc-based macs, including the elimination of one type 11 error. also included were a number of reliability improvements, such as fixes for macs using floppy disks equipped with a dos compatibility card, improved hard disk access for powerpc powerbooks and performa 5400 through 9500 computers, fixes for macs that included an apple tv tuner or macintosh tv remote control, improvements to localtalk and networking (especially for the performa 5400 and 6400), fixes to system startup for the faster 180 mhz macs (which included powerpc 604 or 604e processors), improved reliability when using sound-intensive applications on quadra or centris computers that contained the powerpc upgrade card, and improved stability when using multiple background applications and shared printers on a network. system 7.5.5 is also the last system 7 release that can run on 68000-based macs such as the macintosh plus and macs with roms that lack support for 32-bit addressing such as macintosh iicx. 7.6 and later required a 68030 processor and 32-bit-addressing-capable rom and will automatically turn on 32-bit addressing on boot.