System 7

System 7 (whose codename being "Big Bang", reflects on the considerable changes that came with the OS) is the term used to refer to the Mac OS that superseded the earlier versions known simply as "The System", or "System 6", and before the use of the term "Mac OS" came into official use. The name reflects the version number of the OS&mdash;7.0, but the term is also used to apply to all the 7.x versions.

System 7.0 was released for the Apple Macintosh on May 13, 1991. It offered a number of system enhancements that were either previously not available, or were optional extensions to the operating system.

New Features
Compared with System 6 and earlier, System 7 offered:


 * Built-in co-operative multitasking. Previously this function was available through 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&mdash;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 earier 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 bootup 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 colour" imaging was included as standard&mdash;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.


 * Balloon Help provided on-screen tooltips. A Help menu was added to the menu bar to control it.


 * TrueType, a new outline font technology developed by Apple.


 * A new full-colour user interface was included which gave a neat colour appearance on colour machines but which gracefully dropped back to the standard black and white interface on machines not supporting colour.


 * 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 address space, 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 the earlier systems, the claim was rather hyperbolic. This became somewhat empty over the following years, as stability of the system degraded terribly as the complexity of the systems grew. Later versions of System 7 were notoriously unreliable, often freezing the entire machine 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. Another problem was System 7's 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.

Versions of System 7

 * System 7.0
 * System 7.0.1
 * System 7.1
 * System 7.1.1 (System 7 Pro)
 * System 7.1.2
 * System 7.1.2P
 * System 7.5
 * Mac OS 7.5.1
 * Mac OS 7.5.2
 * Mac OS 7.5.3
 * Mac OS 7.5.3L -- Mac clones only
 * Mac OS 7.5.3 Revision 2
 * Mac OS 7.5.3 Revision 2.1
 * Mac OS 7.5.3 Revision 2.2
 * Mac OS 7.5.4 -- never released
 * Mac OS 7.5.5
 * Mac OS 7.6
 * Mac OS 7.6.1

See also: Performa Systems

Soon after the release of the original System 7 (System 7.0), System 7.0.1 was released with a number of fixes. Next year's System 7.1 introduced the new Fonts folder, allowing users to organise their fonts in the Finder.

A significant upgrade was System 7.1.1, also known as System 7 Pro. This release was basically a bundle of 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 the new functionality.

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 resulted in System 7.1.2, which included a number of fixes and new features as well. This was followed quite quickly with System 7.1.3, primarily a bug-fix release, but which also included, on select PowerBooks, the Control Strip.

The next major release was System 7.5, which rolled up all the fixes from previous versions and added a progress bar during startup and the new Apple Guide help system. Apple Guide was extremely powerful, but tedious to implement due to its power, and few programs supported it. Mac OS 7.5.1 was primarily a bug fix on System 7.5, but also introduced a new Mac OS startup screen in preparation for the Mac clones. A slew of minor versions followed, so many that the name change appeared to stall at Mac OS 7.5.3, and instead added a release number 2, 2.1, and 2.2. With Mac OS 7.5.4 pulled, Apple released Mac OS 7.5.5 on the following day.

Through this period Apple had been attempting to release a completely new "modern" operating system, Copland. When the Copland project was finally killed in 1996, they 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.

Future versions were released as Mac OS 8 and Mac OS 9. Although the differences were largely cosmetic, Mac OS 8.6 introduced a new prementive multitasking nanokernel that replaced the original nanokernel that was introduced when Mac OS was ported to PowerPC, which is the only code that ran in native PowerPC supervisor mode. The multitasking features of the new nanokernel was accessable through version 2.x of the Multiprocessing Services library, which was released at the same time.

Adoption
System 7.0 was adopted quite rapidly by Mac users, and quickly became the base requirements 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 minor upgrades from System 7.x, compared to the changes from 6.x to 7.0.

Lost opportunity?
With the release of System 7, Apple had perhaps lost a great opportunity to make a truly modern microkernel-based OS. System 6 ran in about 600k, much of which was a set of shared code. 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; 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 ready for some time.

In 1995, Apple committed itself to providing a microkernel-based system in the Copland project, which staggered on for two years before finally being killed off. Much of the complexity was due to the terribly complex memory management scheme needed to keep the per-application memory footprint within reason. The complexity was so much that the system was simply never able to stabalise.

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.

Related Articles

 * Compatibility Checker

Sources and References

 * Wikipedia: System 7 (Macintosh)