System 4.0 (Finder 5.4, System Software 2.0.1) was released January 1, 1987.
In fact, System 4.0's major claim to fame would be the fact that it was the first System to exclude a model, the Mac 128k.
It did have some fixes to accommodate AppleShare, including a new Chooser whose looks changed little through Mac OS 9, and a new Control Panel with an AppleTalk section. System 4.0 was recommended for all Macs with 512k of RAM and higher; the Mac 512k and above (including a Mac 128k with the 512Ke hardware upgrade) were able to run it. The system did not have very high adoption before it was replaced by System 4.1 less than two months later.
- The develop CD and its spawn by Eric Rasmussen, Apple Macintosh before System 7. Archived 2011-11-22.
- Dates in Mac history by Lawrence I. Charters and Dr. Kathleen G. Charters, KLJCharters Blog. 2013-10-30.
- System 4.0 (System Software 2.0.1), The Mac 512. Archived 2016-12-02.
- Macintosh: System Software Version History at Apple Support (2012-02-19)