History of Mac OS - System 7

System 7

On May 13, 1991, System 7 was released. It was a major upgrade to the Mac OS, adding a significant user interface overhaul, new applications, stability improvements and many new features. Its introduction coincided with the release of and provided support for the 68040 Macintosh line. The System 7 era saw numerous changes in the Macintosh platform including a proliferation of Macintosh models, the 68k to Power Macintosh transition as well as the rise of Microsoft Windows as a serious competitor, increasing use of computer networking and the explosion in popularity of the internet.

Perhaps the most significant feature of System 7 was virtual memory support, which previously had only been available as a third-party add-on. Accompanying this was a move to 32-bit memory addressing, necessary for the ever-increasing amounts of RAM available to the Motorola 68030 CPU, and 68020 CPUs with a 68551 PMMU. This process involved making all of the routines in OS code use the full 32-bits of a pointer as an address — prior systems used the upper 8 bits as flags. This change was known as being "32-bit clean". While System 7 itself was 32-bit clean, many existing machines and thousands of applications were not, so it was some time before the process was completed. To ease the transition, the "Memory" control panel contained a switch to disable this feature, allowing for compatibility with older applications.

One notable System 7 feature was built-in co-operative multitasking. In System Software 6, this function was optional through the MultiFinder. System 7 also introduced aliases, similar to shortcuts that were introduced in later versions of Microsoft Windows. System extensions were enhanced by being moved to their own subfolder; a subfolder in the System Folder was also created for the control panels. In System 7.5, Apple included the Extensions Manager, a previously third-party program which simplified the process of enabling and disabling extensions.

The Apple menu, home only to desk accessories in System 6, was made more general-purpose: the user could now make often-used folders and applications—or anything else they desired—appear in the menu by placing aliases to them in an "Apple Menu Items" subfolder of the System Folder. System 7 also introduced the following: AppleScript, a scripting language for automating tasks; 32-bit QuickDraw, supporting so-called "true color" imaging, previously available as a system extension; and TrueType, an outline font standard.

The Trash, under System 6 and earlier, would empty itself automatically when shutting down the computer or, if MultiFinder were not running, when launching an application. System 7 reimplemented the Trash as a special hidden folder, allowing files to remain in it across reboots until the user deliberately chose the "Empty Trash" command.

System 7.1 was mainly a bugfix release, with a few minor features added. System 7.1 was not only the first Macintosh operating system to cost money (all previous versions were free or sold at the cost of the floppies), but also received a "Pro" sibling with extra features. System 7.1.2 was the first version to support PowerPC-based Macs. System 7.1 also introduced the System Enablers as a method to support new models without updating the actual System file. This led to extra files inside the system folder (one per new model supported).

System 7.5 introduced a large number of new features, many of which were based on shareware applications that Apple bought and included into the new system. On the newer PowerPC machines, System 7.5 may have had stability problems partly due to a new memory manager (which can be turned off), and issues with the handling of errors in the PowerPC code (all PowerPC exceptions mapped to Type 11). These issues did not affect 68k-architecture machines. System 7.5 was contemporary with Apple's failed Copland effort as well as the release of Windows 95, which may explain Apple's purchase of several shareware system enhancements to include as new system features.