Mac OS 8.1

Released January 19, 1998, Mac OS 8.1 was the last version of the Mac OS to run on Macintosh computers with either a 68k processor, or PowerPC processor.

New features in Mac OS 8.1

 * USB: USB made its big debut.
 * HFS Plus: The new, optional HFS+ Mac disk format, also known as the Mac OS Extended Format, made its debut in Mac OS 8.1. To upgrade, you generally had to wipe out the contents of your entire hard drive before upgrading to HFS+, although some utilities held your data steady while upgrading silently to HFS+.
 * Windows 95 long file names: Mac OS 8.1 had an enhanced version of PC Exchange supporting long file names (255 instead of 31 or 8.3 letters) coming from Windows 95, as well as media such as Zip disks from Windows 95.
 * Reverse-sort button in Finder: A tiny platinum button looking like a pyramid formed by several horizontal dashes made its debut in Mac OS 8.1. This allowed you to reverse-sort the order of the window's content (e.g. Z to A instead of A to Z, etc...).

It is the earliest version of the Mac OS that can run Carbon apps.