Thomas Alexander Stephens 7y
Originally Answered: If Mac OS X and Linux are based on Unix, then what is Windows based on and why was it implemented like this by Bill Gates?
There’s a huge amount of path dependency in how Windows, OS X and Linux came to exist as they are.
In Bill Gates’s initial strategy, devised in the 1970s, Unix was to be the core of the Microsoft platform. Microsoft’s version of Unix, called Xenix, was first released in 1980 (before MS-DOS). It rapidly became the most popular variant of Unix, but like all Unix systems, it required much more advanced hardware than low-end operating systems like CP/M.
MS-DOS was basically a copy of CP/M, which Microsoft acquired so it could license Microsoft Basic to IBM. Microsoft had already licensed Microsoft Basic to Commodore and Apple, so the IBM deal was just one of many, and MS-DOS was not viewed as a strategic OS. It was just a stop-gap until mass-market hardware became powerful enough to run Xenix.
In 1982, a legal earthquake led Bill Gates to completely change Microsoft’s strategy and abandon Unix, despite the fact that Microsoft was the leading vendor of Unix at the time. The earthquake was the breakup of the Bell System. AT&T had licensed Unix so widely, including to Microsoft, because the agreement granting it a telephone monopoly in the US had also barred it from entering the computer or software businesses itself. With the end of the monopoly, that bar also came to an end.
Bill Gates understood that AT&T’s entry would severely weaken all other Unix vendors (as it did, leading to the so-called ‘Unix wars’), so immediately started looking for alternatives. The partnership with IBM provided an opportunity, so Microsoft and IBM agreed to collaborate on a successor to MS-DOS called OS/2.
In addition to OS/2, Microsoft had decided to offer a GUI for MS-DOS, called Windows, to prevent the emergence of a competitive threat before OS/2 was finished. The idea was Windows and OS/2 would have similar GUIs, and Windows would fill the gap between MS-DOS and OS/2.
Another influence came from the hardware side. OS/2 was tightly coupled to the x86 PC architecture, and by the late 1980s it had become widely believed that RISC CPUs would eventually replace the then-dominant CISC architectures (VAX, x86 and 68k). Looking to the future, Microsoft took advantage of management incompetence inside DEC to hire DEC’s best software developers. They were tasked with designing an new OS that could run on non-PC hardware, and would be able to emulate OS/2 as well as MS-DOS and Unix/POSIX. That OS was planned to be sold as OS/2 version 3.0.
While the classic OS/2 failed to gain traction in the market, Windows unexpectedly took off. Windows was less powerful and less reliable, but had the advantages of lower resource requirements, better compatibility with MS-DOS software and better performance on low-end hardware. The success of Windows led to yet another shift in Microsoft’s strategy. To avoid losing Windows developers, Microsoft proposed to add a 32-bit Windows API to NT, which would run alongside the OS/2 API. IBM management feared that a 32-bit Windows API (owned by Microsoft) would undermine the OS/2 API (owned by Microsoft and IBM), so refused.
Faced with the risk of losing Windows developers when the hardware became powerful enough for MS-DOS/Windows to be replaced, Microsoft refused to accept the IBM position. As a result, the two companies parted ways, with IBM taking the classic, PC-only OS/2 2.0 and Microsoft taking NT. A 32-bit Windows API was added to NT, with OS/2 support relegated to 16-bit legacy OS/2 software, and the OS was transformed from OS/2 3.0 into Windows NT.
Windows NT 3.1 was released in 1993, but MS-DOS/Windows 3.x/9x continued to dominate the PC market of the 1990s. The hardware simply wasn’t powerful enough for a more advanced operating system like NT (especially when running legacy MS-DOS software, which ran much faster under the less secure and robust design of Windows 3.x/9x). By the early 2000s, the hardware finally caught up with the software, and Windows NT was finally released in a consumer form, as Windows XP. With that release, MS-DOS/Windows 3.x/9x finally died and the Windows OS as we know it became the dominant PC operating system.
The Apple story is also quite complex, involving Steve Jobs being forced out of Apple, hiring people to develop a Mach-derived OS called NextStep (which originally ran on the 68k architecture), then being brought back to Apple and engineering a reverse-takeover. As with Windows, the classic Mac OS was completely replaced by a new OS, which was marketed under the same name as the old one. It happens that the new OS implements a Unix API (a kernel-mode server for the Mach microkernel), but it’s mostly a derivative of Mach.
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