Only one side will be the true successor to MS-DOS – Windows 2.x

On one hand you have that the technical answer to the above question is likely "yes". DOS is so simple that any non-trivial application likely qualifies as an operating system. Implementing some kind of virtual memory support is almost a given, and process control is not unheard of.

But on the other hand most people would refer to anything pre-95 as "shell" for the simple reason that it requires DOS to boot ; even when complexity-wise, 95 and later versions of 3.x are practically the same: if you call one an OS, you ought to call the other one a full OS too.

So this question is on the "angels on the head of a pin"-level; but this simply means there's no answer that doesn't require a lot of nuance, and this also applies to the "it can't be a shell, it does too many things" answer.

I’m not really going to put any cognitive effort into fully concentrating on something like this to the point where I see that there is something that looks like it might be an expansion button. If I’m supposed to see it, it should be visibly on the page.

Or even "little multitasking" because while Windows had multitasking, we didn't have the HW to do too many things at the same time.

Right now we're on the crazy end of that spectrum. Every tab on your browser is potentially an application, and we multitask like crazy on it.

Do I want to go back to "No multitasking?" Not really. Or at least not all the time. But I definitely want to put barriers. Such as taking a minute to switch windows/applications.

Then you read some "under the hood" book or source code and start stumbling upon decade of hacks upon hacks to keep this cart rolling while computer revolution was happening in the background.

One example: IBM in its infinite wisdom didnt expect to support more than one type of floppy in 5150 BIOS. IVT (Interrupt Vector Tble) has allocated space for only one DPT entry (Diskette Parameters Table), same goes for DBA (Bios Data Area). Few years later 1.2MB 5.25 drives showed up, year later 720KB 3.5 ones and so one. As a result BIOS was forced to play musical chairs under the hood constantly shuffling contents of that _one DPT entry_ replacing it on the fly while trying to keep track of whats going on. Of course DOS needs to run on older PCs without multi floppy format aware BIOS thus 1986 MS-DOS 3.2 introduced DRIVPARM doing exactly the same shuffling one layer above https://jeffpar.github.io/kbarchive/kb/060/Q60091/

DOS was build one small hack at a time. High Memory, Upper Memory, Expanded memory, Extended memory, A20, exit from Protected mode, more than one kind of floppy, hard drive, more than two hard drives, the list of kludges just keeps going.

And OS/2 1.1 was very similar to Windows 2.1, so it's arguable if it was actually much better.

OS/2 1.2 was a massive leap though, not only beating Microsoft GUI wise by a whole year, they even implemented tons of advanced features that we didn't see until Windows 95.

OS/2 1.x's DOS box was bad, with lots of limitations, which isn't good when most existing PC apps are DOS apps. As for GUI, well, lets call the Presentation Manager 1.x v Windows 2.x a no-score draw.

Edit: I spoke to EmeraldDM8, who made the UI, and if it's what he thinks it is, it's because the series page is not done yet, and once it's ready, that will include a link to that page.