Historical Operating Systems – Apple’s System 6

Apple’s approach to the computer market has always rested on its hardware, with a deeply integrated approach to its operating system software which is still obvious even with the Intel-based hardware architecture of today’s Macintosh computers, and the UNIX operating systems used in almost all Apple hardware. In the 1980s, when Apple was one of the biggest customers of Motorola 68k processors and relied on its own proprietary hardware, their integrated approach was even more obvious, with a stylistic approach which stood apart from competitors such as Commodore’s Amiga, and especially stood apart from the distinctly ugly early versions of Microsoft Windows which were found on the myriad of IBM PC-compatible machines in the market.

System 6 was the penultimate revision of the Macintosh System Software designed for Motorola 68k processors. It was released in 1988, slightly after the release of the Macintosh SE computer, an integrated all-in-one unit which resembled the original Macintosh units, along with the Macintosh II, the first of the Macintoshes with a separate monitor, and the first able to display colour images. Ultimately, like its predecessors, System 6 took its provenance from the system software of the original Macintosh 128k, although it had been developed somewhat since then.

The system software of the Macintosh 128k was graphically impressive, but with a single-tasking approach which more closely resembled that of the command-line-based operating systems it was competing against, it wasn’t particularly technically impressive. Given the obvious capacity for a GUI to run more than one program at a time, which was demonstrated on the predecessor to the Macintosh, the Lisa, this was a somewhat disappointing state of affairs. This was only rectified with the release of System Software 5 in 1987 and its MultiFinder extension which allowed cooperative multitasking for the first time.

With the capacity for System 5 and System 6 to run on older machines, this extended the multitasking back to the Macintosh Plus and the 512Ke. Cooperative multitasking was not the optimal way of solving the problem of running more than one program at a time; it relied too much on the voluntary ceding of CPU time by each application, and led to problems such as entire networks slowing down because people held down their mouse buttons for too long. The Amiga, which had been released two years previous, used pre-emptive multitasking, a technically superior option, although one which required more complicated underlying software and which imposed a slight additional load on the CPU. Apple’s operating systems, on the other hand, would end up using cooperative multitasking all the way up to Mac OS 9, and even then had to provide the capability for cooperative multitasking to provide backwards compatibility.

Where System 6 lacked technical sophistication, however, it arguably made up in style. Where the GUI contemporaries of System 6, such as AmigaOS and RISC OS, started off with garish colour palettes and only later developed styles that were more comfortable to the eye, System 6 continued the slow evolution of the interface style that would persist on Apple’s platforms all the way up to the adoption of Mac OS X. With the Chicago typeface across the persistent top menu bar, the familiar Trash can and the iconic Happy Mac and Sad Mac icons, the familiar elements had already been set in place for the standard Mac OS interface for the next ten years.

A typical screenshot from a Macintosh SE – which would still look familiar to users of the latest versions of Mac OS 9.

System 6 came on four 800KB floppy discs, or later on two 1.4MB floppy discs, and the system could be booted directly from the floppy drive, while also having the capacity to be installed on both internally- and externally-mounted hard drives. As the older Plus and 512Ke models weren’t provided with hard drives as standard, and as System 6 officially dropped support for the slow and expensive Hard Disk 20 which had been supplanted by SCSI-based technology in the newer computers, the ability for the operating system to still be booted from the floppy drive gave older Macintosh users the features of the newer operating systems without having to buy completely new machines.

Even with the floppy interface, System 6 is notable for its rapid loading time. Even on the likes of the Macintosh Plus or SE, the operating system will load to a fully-working state in about thirty seconds, more quickly than a modern PC or Mac running the likes of Windows or Mac OS X. This rapid loading time was facilitated by the use of 68k assembly language to program the operating system, unlike its successors which would use C and were not as well-optimised for their individual platforms. System 6 was obviously very tightly integrated with the Macintosh architecture – a situation which would have suited Apple right down to the ground.

Ultimately, though, that tight integration with one processor architecture and one line of hardware couldn’t persist forever. While System 7 would run slower on any 68k-based Macintosh than System 6, and could no longer be booted from a single floppy disc, it was portable to the PowerPC processors which Apple had planned for its computers since 1991, and finally adopted in 1994. System 7 also had support for 32-bit memory addresses, rather than the limited 24-bit addresses of System 6 – limiting it to a scant 8 megabytes of RAM. While System 6 would run smoothly on a late-1980s or early-1990s Macintosh, its limitations weren’t in keeping with Moore’s Law.

Today, System 6 is one of the revisions of Mac OS Classic provided for free by Apple on its support website. The North American versions of System 6.0.3, 6.0.5 and 6.0.8 are provided as compressed StuffIt Expander images which can be expanded into four 800K or two 1.4MB floppy images. These images, once extracted, will work in various emulators of Macintosh systems, as well as providing users of old Macintosh systems a way to keep their systems going even if their original system discs stop working. It’s difficult to find many other operating systems from this time period – both AmigaOS and RISC OS are tightly controlled by their owners, while Windows versions predating Windows 3.1 are barely worth trying – so this is an interesting chance to see what GUIs looked like from the non-PC-compatible side of the fence.