System 7 (Macintosh)

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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"Big Bang", reflects on the considerable changes that came with the OS) is the term used to refer to the Mac OS that superseded the earlier versions known simply as "The System", or "System 6", and before the use of the term "Mac OS" came into official use.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—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.

Compared with System 6.x and earlier, System 7 offered:

• Built-in co-operative multitasking. Previously this function was available through MultiFinder in System 6.0, 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 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 earier system versions.

• 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.

• 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.

• 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.

• 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.

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. 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 7.0 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.

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.

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