System 4

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

System 4.0

 * Was a minor update from System 3, but did have some changes and new features.
 * Introduced AppleShare client, to connect to file servers, as part of the OS.
 * Updated the LaserWriter Driver to 3.3.
 * Included with the Macintosh SE.

System 4.1

 * Updated the LaserWriter Driver to 4.0.
 * Included with the Macintosh II.

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.

Release history

 * System 4.0 — January 1987
 * System 4.1 — April 1987
 * System 4.2 — October 1987
 * System 4.3 — November 1987