Windows in 1983?
Wiki's article says November '85. God, that predates OS/2! But the first worthwhile version of Windows (3.0) turned up in 1990.
RISC OS is from 1988, but before that came Arthur in June 1987. It is a bit bogus to throw in a comparison with *Unix*, so at least be honest and say X came about in 1984, while the current X11 was released in September 1987 (nerrr! after Arthur :-) ).
I wonder - if Win3 was co-operative multitasking, and Win32 (95, etc) was pre-emptive, I wonder how much was 'kludged' so a PMT OS could handle CMT applications? Let's not forget that Win32 was [supposed to be...] 32 bit, while many of the older applications were 16 bit. I can still run Win3.1 apps on XP. Useful, but also a bit disturbing. My main gripe with W95 was how often the damn thing used to bluescreen. Long gone days, it takes a *lot* to get XP to bluescreen. I think I've had my eeePC for nearly a year now, hasn't BSOD'd on me once. [this, of course, is tempting fate, isn't it?]
But, then, having said all of this, there are good reasons to want to keep RISC OS alive. It is a simple OS, simple to understand, simple to use. It is highly modular, I mean, hell, the entirety of the OS beyond the core kernel is a bunch of "modules". It is powerful and feature-laden for its size. RISC OS fits on a 4Mb ROM (later versions use a bigger flash because I think it is circa 5Mb). How big was Windows 3.11? How big was Windows 95? My Neuros OSD PVR came with a version of Debian installed in a 16Mb flash. If you update to the latest firmware, it resides (permenantly) on a CF card because it outgrew the flash space. Of course, it makes it easier to run a live filesystem than all the read-only flash stuff, but still... If I ever succeed in porting any version of RISC OS to the unit, I fully anticipate being able to softload it into the OSD's memory (32Mb, I think) and running with it there in-situ. Pare it down a little bit (as Neuros did to the Debian), I don't see why it wouldn't fit in a teeny-tiny 4Mb.
And finally (yes, I am known for long rambling posts, so there's light at the end of the tunnel now!), substantial parts of the core OS were written in assembler by the very people involved in the design of the processor it is running on. Howzat for speed freak satisfaction? RISC OS demands little but gives a lot. It may be lacking in modern codec support, but I think that is only due to it never really being used in a CPU/DSP system. There doesn't seem to be any technical reason why you couldn't design some sort of media player running on RISC OS - you'd only ever see the media player interface anyway. Perhaps why Linux is used more is because Linux is truly open in the OPEN sense of the word. RISC OS is only partially open and... is it ALL available yet, or are there still bits missing? They've only just published FPE's sources...