Not quite. Yes, Win 9x uses MS DOS as a bootloader, but once 32-bit Windows is running, it replaces all the functionality of DOS. It does a few crazy things for handling stuff like real-mode drivers, but I don't know all the technical details off the top of my head.
It doesn't have nearly the security features of NT, but 9x has some limited memory protection and preemptive multitasking. It's certainly worlds more sophisticated than the classic Mac OS all the way up through Mac OS 9, which was barely more than a loose collection of libraries tied together with a standard calling convention based on the notion of "traps". It had essentially zero memory protection or preemptive multitasking, which is why you'd usually have to reboot a Mac whenever anything went wrong. Fortunately, OS X changed all that.
I wish I had a good source; I've had my current one for several years now. I think I must have bought it shortly before they discontinued that line.
There's a no-name clone of the DBC-150 selling for about $10 on Amazon. I bought one out of curiosity, and it's not too terrible. The scheduler is pretty much the same, and you can store longer text strings than the Casio allows, but it's missing world time, and doesn't have a proper countdown timer. Also, the light is almost useless. The raised buttons actually improve tactile feedback, but I can't say what their long-term durability is like.
"Sir, I think there's a problem with our calculations."
"Uh... uh... dark matter! Yeah, that's the ticket!"
Sure. We'll sell to pretty much anybody, from a garage hobbyist, to a global corporation.
We've got a pretty sizeable warehouse full of previous-gen (and current gen) goodies, which is why I can throw together a test rig on very short notice, and for comparatively little cost. I think our sales and purchasing guys can track down REALLY old stuff, if you've got some ancient Sun gear you need to keep running.
Disclaimer: I work for them, but I'm not an official company spokesperson. All of this rambling is purely my own views and opinions.
I work for an IT hardware reseller (mostly; we do some new stuff too), so scrounging up some lab boxes or test beds usually isn't a problem. I've got one in our rack right now that I fire up to mess with VMs via Hyper-V, rather than adding a bunch of extra load to our ESX cluster. And we mostly deal with smaller development projects, not spending months building huge software packages, so it's generally not too hard to grab a few hours of downtime here and there to read and experiment with stuff. Our dev team (a whole two of us) have MSDN subscriptions, so it's open season on learning MS products and figuring out what might be useful to us.
Thus, I don't have a ton of experimental IT gear at home, nor do I feel all that compelled to continue doing at home what I do all day at work. I've got a desktop that does a few light server duties, and which is mostly just a means to and end. I do have a growing pile of assorted tablets, though...
Some people have a great ambition: to build something that will last, at least until they've finished building it.