The 1.4MB and 800k versions of System Update 3.0 are exactly the same, but on different size disks. There are some Macs that can run System 7.1, such as the Mac Plus, early SE's, and Mac II which only have 800k floppy drives, so Apple had to release disks for those Macs. Your PowerBook 180c has a 1.4MB drive, so you're best off going with the 1.4MB version, which requires less disks.