System 7 (whose codename being "Big Bang" reflects the considerable changes that came with the OS) refers to the Mac OS that superseded "The System" or "System 6" before "Mac OS" came into official use. The name reflects the version number of the OS—7.0, but the term is also used to apply to all the 7.x versions, both those labeled "System" and those labeled "Mac OS."
System 7.0 was released for the Apple Macintosh on May 13, 1991. It offered a number of system enhancements that had previously been absent, or only available as optional extensions to the operating system.
- Built-in co-operative multitasking. Previously this function was available through the MultiFinder in System 6, or not available at all. Because more than one application could run at a time, Desk Accessories were deprecated, System 7 treating them no different from other applications.
- The Trash was now a real folder instead of the special status it previously had. This allowed items to be put in the trash on different volumes, each one having its own Trash.
- Personal File Sharing. Along with various user interface improvements for AppleTalk setup, System 7 also included a basic file sharing server allowing any machine to publish folders to the AppleTalk network.
- The Control Panel became the Control Panels — they became individual "windows of options" accessible from the Control Panels folder in the Finder, instead of being accessible using the previous Control Panel Desk Accessory in earlier system versions.
- In a similar fashion, system "extensions" were also improved by placing them in their own folder (rather than the System folder's root), and holding down the Shift key during boot-up would disable them. The line between extensions and control panels was blurred, extensions basically being GUI-less control panels.
- Aliases: small files that "pointed to" other files on the system. This was added to help the user navigate the increasingly larger disks that were starting to appear.
- The Apple menu (previously home only to Desk Accessories pulled from DRVR resources in the System file) now listed the contents of a folder, including aliases. Desk Accessories had originally been intended to provide a form of multitasking and were no longer necessary now that multitasking was always enabled. The desk accessory technology was deprecated, with System 7 treating them largely the same as other applications.
- Application menu. A list of running applications, formerly at the bottom of the Apple menu under MultiFinder, was moved to its own menu on the right, along with Hide and Unhide functionality.
- AppleScript. This was an entire architecture for making scriptable applications. While fairly complex for programmers to implement, this feature was powerful and popular with users, and is still available to this day as part of Mac OS X.
- 32-bit QuickDraw, supporting so-called "true color" imaging was included as standard—it was previously available as a system extension.
- Publish and Subscribe. This feature permitted data "published" by one application to be imported ("subscribed") by another, and the data could be updated dynamically. The feature was not terribly popular with programmers, who found the API unwieldy, and users didn't seem all that interested either. Relatively few applications ended up adopting it.
- TrueType, a new outline font technology developed by Apple.
- A new full-color user interface was included which gave a neat color appearance on color machines but which gracefully dropped back to the standard black and white interface on machines not supporting color.
- A new Sound Manager API which replaced the older ad-hoc APIs that did not abstract the hardware to any great degree. (This was also included with System 6.0.8.)
- System 7 started to pave the way to move to a full 32-bit addressing system, from the previous 24-bit address space, which limited memory to a maximum of 8MB. 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 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. Additionally, "32-bit dirty" (i.e. non-"32-bit clean") Macs no longer ran any version of the system software as of version 7.6.
There were also a large number of architectural changes to make the OS more coherent and stable. Apple boasted on its release that System 7 was "rock solid", and while it was a great improvement over earlier systems, the claim was rather hyperbolic. This claim became somewhat empty over the following years, as stability of the system degraded terribly as the complexity grew. Later versions of System 7 were notoriously unreliable, often freezing the entire machine and corrupting filesystems after benign application errors. In particular, before Mac OS 7.6.1, almost all errors caused by a PowerPC application caused Type 11 errors and so caused the whole system to crash.
Many also felt that performance suffered as a result of upgrading from System 6 to System 7, though new hardware soon made up for the speed loss. System 7 also had a comparatively large "memory footprint"; System 6 would run on a single floppy and took up about 600k of RAM, whereas System 7 used well over a megabyte and could no longer be run from floppy-only machines. It was some time before the average Mac shipped with enough RAM built-in for System 7 to be truly comfortable.
Soon after the release of the original System 7 (System 7.0), System 7.0.1 was released with a number of fixes. The next year, System 7.1 introduced the new Fonts folder, allowing users to organize their fonts (and other System resources) using the Finder instead of ResEdit or Font/DA Mover.
System 7.1.1, also known as System 7 Pro, was a significant software upgrade for 7.1 users. It bundled System 7.1 with AppleScript tools, QuickTime and PowerTalk (AOCE). While System 7 had troubles running in slightly older machines due to memory footprint, System 7 Pro would barely fit into even the most "loaded" machines of the era. Most users installed it for various minor fixes, ignoring or even removing the new software.
Soon after the release of System 7, Apple joined the AIM alliance and started work on PowerPC-based machines that would later become the Power Macs. Support for these machines arrived in System 7.1.2, which also included a number of fixes and new features for 68k Macs. This was followed quite quickly with Finder Update 7.1.4, which did not actually update the System file but was primarily a Finder bug-fix release that also included the Control Strip on select PowerBooks. As a result, the latest version of System 7.1 was System 7.1.2 with Finder 7.1.4.
The next major release was System 7.5, which rolled up all the fixes from previous versions, added features from the Performa fork of System 7.1, plus added a progress bar during startup and replaced Balloon Help with the new Apple Guide help system. Apple Guide was extremely powerful to use, but tedious to implement due to its complexity, so few programs supported it. Mac OS 7.5.1 was primarily a bug fix for System 7.5, but also introduced a new Mac OS startup screen to highlight the OS as separate from the computer in preparation for bundling on the Mac clones. A slew of minor updates followed, but the version number appeared to stall at Mac OS 7.5.3, with Apple adding release numbers 2, 2.1, and 2.2 (which came in two revisions). After having to pull Mac OS 7.5.4 from production during factory duplication due to a critical bug, Apple released Mac OS 7.5.5 on the following day.
During this period Apple had also been attempting to develop a completely new "modern" operating system, with milestones named Copland, Gershwin and Rhapsody. When the Copland and Gershwin projects were finally killed in 1996, Apple announced plans to release an OS update every six months until Rhapsody shipped. Two more releases were shipped, Mac OS 7.6, and the minor bug fix Mac OS 7.6.1, before Apple scrapped the plan, rolled what it could scavenge from Copland into Mac OS 7, and released the result as Mac OS 8.
Future versions of the System 7 architecture were released as Mac OS 8 and Mac OS 9. Although the differences from System 7 were largely cosmetic, Mac OS 8.6 introduced a new preemptive multitasking nanokernel that replaced the original nanokernel introduced for PowerPC Macs in System 7.1.2. The new nanokernel was the only part of the Mac OS that ran in native PowerPC supervisor mode. The multitasking features of the new nanokernel were accessible through version 2.x of the Multiprocessing Services library, which was released at the same time as Mac OS 8.6.
System 7.0 was adopted quite rapidly by Mac users, and quickly became the base requirement for new software. Until the advent of OS X, System 7 was by far the largest shake-up and revamp of the Mac OS since its inception. Mac OS 8 and Mac OS 9 were relatively superficial upgrades from System 7.x, compared to the changes from 6.x to 7.0.
With the release of System 7, Apple lost an opportunity to create a modern microkernel-based OS. System 6 ran in about 600k, much of which was a set of code shared with running applications. It seems entirely possible that an operating system running multiple independent System 6 "boxes" could have been built that would have run in about the same memory footprint as System 7. Under such a model, the operating system would be able to gracefully exit misbehaving programs without causing the system as a whole to crash. It would have also provided the groundwork for a new application model designed specifically for the new OS.
Instead, System 7 was really an extensive collection of "bells and whistles", dramatically improving the look and feel of the system, but doing little "under the hood". A similar "run multiple 7s on a kernel" would simply not work, as System 7 was so much larger than System 6. Additionally, one key part of the entire Mac OS, QuickDraw, was not able to be used effectively in a protected memory system (for performance reasons it stored state in each application's memory). Although a new version of QuickDraw could have been written, empire building placed all such efforts under the QuickDraw GX project, which was not completed until years later.
In 1995, Apple committed itself to providing a microkernel-based system in the Copland project, under which engineering chased an ever-changing marketing-driven feature list for two years before the project was finally killed off. Much of the complexity of Copland was due to the terribly complex memory management scheme needed to keep the per-application memory footprint within a reasonable size. The complexity was so great that a stable version of the development system was never released.
Project Star Trek was an attempt by Apple and Novell to port System 7 to x86 machines -- where the OS had never gone before. While the team successfully made it boot on a 486, the project was controversial inside Apple, and was cancelled without ever being made into a commercial product.
The Blue Meanies
The coding group within Apple responsible for System 7 were known as the "Blue Meanies" after the blue slips of paper on which were written the features that could be implemented in a relatively short time. In comparison, the pink-slipped features were handled by the Pink group, later becoming the ill-fated Taligent project. Despite the idea of System 7 being the "quick win", it was still delivered several years late.
- Macintosh: System Software Version History (through 7.5.3), Apple Support. 2012-02-19.