Mac OS 7.5.3 Revision 2.1

Mac OS 7.5.3 Revision 2.1, also known as System 7.5.3 Revision 2.1, was released by Apple Computer on August 5, 1996 with the Macintosh Performa 6400.

Background
The Performa 6400 required a new version of LocalTalk DMA, and the video driver necessitated a fix to correct an error involving a 15-inch monitor when the Mac was going to sleep. The 180 and 200 MHz models of the Performa 6400 were released in August 1996 with Revision 2.1 pre-installed. No other Macintosh required this revision, regressing from Apple's goal for unified OS deployment that had just recently begun with Mac OS 7.5.3 Revision 2.

Mac OS 7.5.3 Revision 2.2 was also released for the Power Macintosh 9500/200 before releases were once again unified with Mac OS 7.5.5 in September 1996.