I know you've already told me DOS could not be ported to x86 for example because it had no multi-tasking. And the same applies to Win1.0-3.0 so they had to make NT. BUT: then why did they make Win95,98,ME?

Multi-tasking support has nothing to do with portability. Why Microsoft made Windows 95 etc. is yet another question, but the paragraph starting with “Both operating systems …” should give some idea.

"When development started in November 1989, Windows NT was to be known as OS/2 3.0, the third version of the operating system developed jointly by Microsoft and IBM. [...] Windows 3.0 was eventually so successful that Microsoft decided to change the primary application programming interface for the still unreleased NT OS/2 (as it was then known) from an extended OS/2 API to an extended Windows API. This decision caused tension between Microsoft and IBM and the collaboration ultimately fell apart." (wiki)

That’s a very useful quote, thanks @TomasBy!

@StephenKitt I missed that paragraph. Ok so the answer is found: NT was for faster PCs and 9x for slower ones.

@zomega yes, and also to address perceived competitive threats from MacOS (hence the revamped UI in Windows 95, which only became available as an extension to NT 4 and properly in 2000).

Now I could ask why it wasn't possible to make one OS that runs both on fast and slow PCs but I think we shouldn't go to deep. It was simply Microsoft's idea behind it.

A richer system needs more resources. It's as simple as that. It's not that anyone wanted NT to not run on a 486 with 4MB, it was just that it couldn't (or at least, not without intolerably poor performance).

@zomega: It wasn't so much about fast vs. slow as it was about how much memory was needed, and (with early versions) what sort of work you were doing. NT could supposedly run in only 5MB of RAM, but I'd say a practical minimum was 16 MB. Before NT 4, support for games was pretty poor as well (previously supported OpenGL, but not Windows gaming API (that was eventually named DirectX).

@Jerry a colleague of mine wrote a couple of OpenGL games on NT 3.51, but yes, NT 4 was much better for games. (And my comment above isn’t quite right — NT 4 shipped with the Windows 95 UI, it was 3.51 that had it as a beta towards the end of its life.) The documented memory requirements were 12MiB minimum in NT 3.1.

@StephenKitt: yeah, that beta was the "shell technology preview" (STP) and NT 4 was originally called the "Shell Update Release" (SUR). The documented minimum was 12, but there was an article at the time (probably in MSJ, but I don't remember for sure) showing that it could actually boot in only 5. I suspect booting in 5 is was completely useless though (may easily have taken an hour of swapping to finish booting, and then couldn't run anything).

Pretty sure I ran NT4 on an 8MB system at one point, although that would have been achieved by downgrading the memory after installation (I had a SIMM fail and couldn't get a replacement quickly), and as I always cut down on unnecessary services immediately after installation it probably wasn't a fair test. Similarly, I ended up using XP on a 40MB system for a while, which with enough services disabled was actually surprisingly usable.

Good answer overall. It might be useful to emphasize that in the 'server' space, Microsoft had nothing before NT; the competition there was Unix, as you mentioned. Some accounts say that GUI support was somewhat of an afterthought for Cutler. That enterprise focus was of course in line with what Cutler had been doing in DECwest

@another-dave there was LAN Manager...

True, but it seemed to me that was at the level of 'file sharing for a small office', not enterprise-y stuff, and in any case ran on a dedicated OS.

@another-dave there was a bit more to it than that (for example LAN Manager introduced domain controllers, IPC using netpipes or mailslots, and supported remote program execution); I’m not sure NT really outgrew LM until NT 4 Server, but NT 4 Server certainly left LM in the dust (cluster services, terminal services etc.).

Was any platform other than x86 (32 or 64) supported in the 00s? There is Windows Phone 8, showcased in 2011, but reading through Wikipedia, nothing in the 00s. If not, it seems amazing to see the portability still there after a decade of unuse.

@jaskij: Windows Mobile (and PocketPC), on the Windows CE kernel. Microsoft really dropped the ball when they let Apple falsely claim they had the first smartphone with apps, and then dropped the ball again when they made Phone 7 incapable of running the millions of existing WM apps.

@jaskij: Ahh, if you're asking about non-x86 platforms that the NT kernel supported in between Alpha and ARM, you have Itanium.

There's some interesting stuff in that PCMag, once you get through all the ads. It seems 1993 was the year of the Unix Desktop ;)