System 4

System 4 is the fourth major upgrade of the Macintosh system software. System 4 was first released in January 1987.

Features
System 4.0:
 * Was a minor update from System 3, but did have some changes and new features.
 * Introduced AppleShare, a file server, as part of the OS.
 * Updated the LaserWriter Driver to 3.3.

System 4.1:
 * Made for the release of the Macintosh II and SE.
 * Updated the LaserWriter Driver to 4.0.

System 4.2:
 * Improved the "About the Macintosh" dialog box; now contained RAM usage as seen through Mac OS 9.
 * The Color menu was displayed on color capable Macs.
 * Backgrounder, DA Handler, Early Access, and Print Moniter were added.
 * Cooperative multitasking via MultiFinder was added.
 * Updated the LaserWriter Driver to 5.0.

System 4.3:
 * Updated the Apple HD SC Setup partitioning software.
 * Updated the LaserWriter Driver to 5.1.

Versions of System 4

 * System 4.0
 * System 4.1
 * System 4.2
 * System 4.3