[citation][nom]nounamaa[/nom]ta152h: "OS/2 was the closest at it, being much faster than NT, using less memory, and having excellent DOS compatibility. "Then why didn't it succeed?[/citation]
OS/2 1.x was made for the 286, due to IBM's insistence on it, since they were selling a lot of 286 machines, and, felt the 386 wasn't going to be mainstream soon enough.
The 286 had two modes, Real and Protected. Real mode was really a super fast 8086, Protected Mode offered memory protection, virtual memory, 16 MB of memory, etc... OS/2 was written in 286 Protected mode, initially.
The 286 started in Real mode, but could be easily switched to Protected Mode. The problem is, you couldn't switch it back. This is why Bill Gates called it a brain-damaged processor, although in fairness to Intel, they had no idea when the 286 was being designed it would be so important. In fact, it as incredibly fast (there's never been a jump like it since), and did offer compatibility, enormous amounts of addressable memory, virtual memory, and ability to protect applications from each other. A very, very enhancement from the previous design.
OS/2 1.x did have DOS Compatibility Box, but it wasn't great, and you could only open one application up at a time. In fact, we called it the "Penalty Box". OS/2 1.3 was the last 286 release, and in my opinion, outside of MVS, the most stable operating system I have seen. We had servers run for years without being rebooted. But, it still could not run DOS well.
By now you're thinking, if you needed the processor to run in Real Mode for a DOS app, and you couldn't get the processor to switch to Real Mode, how was it possible to have the Penalty Box? Well, you'd basically have to reset the processor, and since it came back in Real Mode, you could do it. They actually used the keyboard processor to help it recover. So, it was really an ugly way to do it.
Microsoft had Windows then, which was really a joke, but it was designed for the 386. Keep in mind, almost every application was written for DOS back then, so even though Windows had none of OS/2's features, it did have better DOS compatibility by virtue of supporting the 386. The 386 had two additional modes, the 386 Protected, which was a 32-bit version (which allowed 32-bit segments as well, which was very welcome) of the Protected Mode, which was renamed "286 Protected Mode", and another very important mode called "Virtual 86". Virtual 86 allowed the 386 to have multiple Real Mode sessions open at once, so in effect you could have several DOS sessions open in different Windows. Because of the shortcomings of Windows, you could not really multitask them well, because it only supported "Cooperative multitasking", meaning it was up to the application to hand over control, as opposed to pre-emptive, where the operating system handles time slicing. So, if was far from perfect, but it still offered considerable advantages over the Penalty Box.
Because of this advantage, and since most people generally needed to run their DOS applications better, people bought Windows, even though it sucked. OS/2 was far more reliable and stable, and multitasked properly, but it didn't run DOS apps as well. So, with people first buying Windows to run DOS apps, they developed a large installed based, and then software companies started writing apps for Windows.
OS/2 2.x and later supported the 386, and offered excellent DOS compatibility. It was called "A better DOS than DOS, a better Windows than Windows", since it could run DOS and Windows apps. In fact the first claim was true, the second was not, but wasn't too far from the truth. But, by the time OS/2 2.x came out, it was too late, Windows had a dominant market share, and although OS/2 made some inroads, it was just too late.
By the way, Windows NT was originally called OS/2 3.0. It was supposed to be a platform independent version, and it was for a while, but since x86 is dominant now, there's only that version. Sadly, they couldn't copy the OS/2 interface, since that was proprietary IBM, and Microsoft and IBM had split up before OS/2 2.0 came out (IBM was annoyed at Microsoft for aggressively supporting Windows, since OS/2 was a joint project for the companies, and the agreed upon future operating system).
The OS/2 interface was remarkable; everything was an object, and was treated the same way. There was also a standard interface design, SAA, that was supposed to be followed for any applications developed for OS/2, and really other operating systems as well. And after you were ready to release the app, there was the SAA police to look it over and make sure it complied
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So, the reason OS/2 didn't succeed was the decision to make the early releases 286 based, and the consequent issues with DOS compatibility. It was a very good operating system, although it had a shared message que which was a big mistake.
Anyway, sorry for the long post, but you asked ...
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