System 3, released concurrent with the Mac Plus, brought several new
features including HFS (Hierarchical File System) and SCSI (Small
Computer System Interface). It is one of the most significant
evolutions in the Mac operating system, second (or perhaps third) to
the advances made with Mac OS 7. System 3.1 was a rare misstep for
Apple, and was quickly replaced with System 3.2 which fixed many of
the previous releases' bugs.
