I own volumes 1, 2 and the PC version. I can vouch for the quality and understandability of the code. I've read a number of operating systems books, and I've found volume 1 to be one of the most straightforward - if you can get past the fact it's written with the PDP-11 in mind. I bought the PC version on a whim after reading volume 1, and found it to be lacking in a number of ways, using BIOS for many system services and glossing over memory protection (not surprising as it targeted the 8086).

One of the more interesting things about Xinu is that its security model is ring based, and if I remember right, it takes advantage of rings 0-3, unlike many modern operating systems. I can't actually remember if the PDP-11's hardware supported this, or if it was emulated by the kernel.

One of my rainy day projects has always been to get Xinu up and running on a PDP-11 emulator - too many operating systems, too little time.

OS/2 was another one using multiple rings.

Interestingly VirtualBox takes advantage of x86's multiple rings: http://www.virtualbox.org/manual/ch10.html#idp12629776 (which contains other interessting details about VirtualBox, like the disassembles and patches code running in the VM in certain cases)

Just to point out another title edit by the mods. The original title was 'Xinu is not Unix'. Considering that's the first line of the body copy it was hardly excessive editorialising in need of fixing and actually did a better job of setting expectations than the pedestrian replacement title.

These mods seem too much like bots lately. Maybe they are?

If HN wants to force use of the <title> element as the post title, why not just auto fill it from the URL and disable editing? it seems silly to offer an editable field whose contents are auto-discarded.

"Xinu Is Not Unix" - also gives more information than "The Xinu Page". Hence, I used it. If you don't feel OS-ey then you may skip the link!

So while you can download code, the real description is in a book, not online, and you can't see it without paying money. Uninspiring.

This is exactly the kind of thing that inspired Linus to make Linux.

Sweet ram o' the rod, a name from the mists emerges.. It has been a long time since I played with Xinu, at least before Linux came to rule the roost .. someone remind me, though, doesn't Xinu have its own compiler onboard, i.e. why do we need two machines, just to bootstrap? Once booted, does a Xinu machine have all it needs to build an image for another Xinu machine?

I guess its a matter of taste, but this dusty beard reckons its not Unix if you're not building another Unix with it. ;P]

Fun and completely irrelevant fact: "Xinu" is the name of the God of Pain in a popular Swedish role-playing game (pen and paper). See here: http://translate.google.com/translate?sl=sv&tl=en&js...

I was directly involved in one of the "industry" projects mentioned on this page. It's great to see Comer's work still around and kicking. XINU was a pleasure to work with.

Our company's lawyers also loved XINU because of the license. The GPL scared them so much we had to take Linux off the table.

X is not UNIX (XNU), GNU is not UNIX (GNU), there are quite a few OSes that aren't Unix.

Heck, even UNIX is not UNIX: https://encyclopediadramatica.se/UNIX

The thing is, that page is better than half of all the unix guides I've seen online.

Except for the `su -c rm -rf /*` part, of course.

The cool part is - UNIX not is XINU

Don't you mean 'XINU ton si UNIX'?

'XTSU' just doesn't have the same ring to it.

UNIX <> XINU

I have fond memories of using Xinu in Dr. Comer's OS course back at Purdue. It's a nice little OS! (and he's a great prof!)

I was scratching my head where I'd heard that name .... and it came to me! Scientology. puke.

I thought that was Xenu.

Don't they pronounce the same in your head? To me they do.

Not in my head, no. Not being a native English speaker may contribute to that.