umount's still there, and it works the same way it does on other UN*Xes - i.e., if some program has a handle (file descriptor, mapped file, etc.) on the volume to be unmounted, it fails (unless you use the -f flag, to forcibly invalidate those handles and unmount the file system). "diskutil unmount" sends a "hey, could you please let go of any handles you have for this?" request before the actual unmount() call is done, and waits a while for "OK, I've released it" replies before it attempts to unmount.

Unfortunately, a lot of stuff in macOS holds onto those handles - and some stuff just grabs them for the lulz as soon as something's recognized as having been mounted - so, as the umount(8) manual says, "Due to the complex and interwoven nature of Mac OS X, umount may fail often. It is recommended that diskutil(1) (as in, ``diskutil unmount /mnt'') be used instead."

(And it's not in POSIX; it's considered an administrative tool and UNIX(R) systems are allowed not to have it or to implement it as they choose.)

Actually, as I said in another post, they don't even "have" to release all of the OS code.

...XNU, the C library, a bunch of kernel extensions, and so on.

...assuming that the code to support the Mac hardware in question is in the kernel, or an open-source kernel extension ("loadable kernel module" in Linux-speak), rather than in a non-open-source kernel extension.

Well, Mach+BSD, but both are open source.

Some of userland is GNU (and some of it may be GNU in various of the *BSDs). Other parts of userland are also from BSD, or written by Apple, or code from various other places. The toolchain, if by that you mean "the compilers, the assembler, and the linker", aren't GNU any more or were never GNU. The assembler and links are from Apple (some possibly ultimately from NeXT); the compilers used to be from GNU, but they're now from the LLVM project.

Not true. They don't have to release a lot of it; for example, the XNU kernel is licensed under BSD licenses, the BSDish license under which Mach was released, or the APSL, none of which oblige Apple to release any of it.

MacBook Pro, or Mac Pro?

Sentence 1 says HFS won't work. Sentence 2 says it will work. In which of those sentences should "HFS" have been something else, and what should it have been in that sentence?

The old line printers didn't do any drawing of pixels, they just had a hammer slam a piece of metal, with a character formed on it, against a ribbon, hitting a piece of paper. The laser printers like the IBM 3800 just let the processor in the printer draw all those bits, rather than doing it in the main CPU.

(And, in a file, an A is still just an A, these days - although if it's UTF-16, it's two bytes rather than one. Those pictures aren't stored in most documents.)

And sometimes it goes the other way; the IBM z13 microprocessor cracks z/Architecture instructions into micro-ops and schedules and executes the micro-ops, just as the Pentium Pro and later x86 microprocessors do.

But you're probably referring to system architecture characteristics, in addition to CPU characteristics.

(Speaking of system architecture characteristics, the z13 has I/O instructions to bang on PCI space, so you could plug PCI devices in and have minicomputer/microcomputer-style drivers, rather than doing I/O over a traditional data channel. They're not documented in the Principles of Operation, but they're used in some of the Linux code for z/Architecture.)

As the NASA document you cite (HTML FTW!) says, it's "an advanced propulsion physics laboratory, informally known as "Eagleworks"" being implemented by NASA Johnson Space Center (NASA/JSC), so it is part of NASA.

You have guessed incorrectly (I was looking at the screen when I typed this). Go back and examine your premises and discard those that led to this conclusion.

Given that it does have a headphone jack (look under "Charging and Expansion"), will you be buying it?

Yes - there were several scenes in the video of the Apple event showing a virtual key labeled "esc" on the left-hand edge of the touch bar (although, as I've noted elsewhere, it's not directly above the {~ `} key, which may get in the way of muscle memory).

I guess you didn't watch the video of the Apple event, where the touch bar had, in many scenes, a button on the left hand edge marked "esc". (As I said in comments for the rumor article, it's not directly above the {~ `} key, so your muscle memory may have some issues with it.)