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I have to admit, DOS memory management is very fascinating to me as a very amateur kernel investigator. I have a book called “DOS beyond 640k” which describes all sorts of extensions people back in the 80s invented to get as much free memory as possible. The contents of course are irrelevant nowadays, but it is still interesting to read as a tech book.
Lacking a discussion on protected mode; the means to access the 1MB+ area (up to 16MB in 286, and 4GB in 386 and later).

https://en.wikipedia.org/wiki/DOS_Protected_Mode_Interface https://en.wikipedia.org/wiki/Virtual_Control_Program_Interf...

I remember toying with DPMI in assembler.

Good times. Our DOS game PaybackTime 2 was only capable of using conventional memory. That was a major reason for the game really not having any proper animations for its player characters.
No discussion on the topic would be complete without QEMM:

* https://en.wikipedia.org/wiki/QEMM

I set up a computer for an engineering department. It was an IBM PS/2. They wanted to run AutoCAD and Ventura Publisher, one used extended memory and the other expanded.

I ended up making batch files that swapped around autoexec.bat and config.sys files so they could run.

'MZ' has been confirmed to be the initials of Mark Zbikowski, there's no question about it. It's not "Memory" + "Last".
Given the MZ magic bytes in the EXE format header - see https://en.wikipedia.org/wiki/DOS_MZ_executable, I would have assumed an association with Mark Zbikowski as well.

The ARR is probably Aaron R Reynolds (also associated with the AARD code for detecting non-MSDOS environments), but you can't ask for his opinion since he passed about 20 years ago - https://www.reed.edu/reed-magazine/in-memoriam/obituaries/no....

Also https://en.wikipedia.org/wiki/AARD_code and a Raymond Chen story involving aaronr - https://devblogs.microsoft.com/oldnewthing/20190924-00/?p=10... and a pic of him with the Windows team - https://web.archive.org/web/20191014055254/https://community...

from another os2museum.com article about MS-DOS, https://www.os2museum.com/wp/dos/dos-3-0-3-2/

  The development of DOS 3.0 was led by Mark Zbikowski and *Aaron Reynolds*, both experienced DOS 2.x programmers.
Confirmed by a Hacker News rando. Seems legit.
How about "confirmed by Mark Zbikowski himself in a video interview"? Does that sound better?

https://youtu.be/c6yPoWrdjkU?si=hxvXTE6ZsdvJs5U9&t=1266

(roughly 21:06 into the video)

That's talking about the MZ signature at the start of every DOS EXE executable (and therefore every Windows EXE as they have DOS stubs), not this additional use as markers in the DOS memory management code. Which probably is also Mark Zbikowski using his initials, but doesn't seem to be confirmed.
OK, fair enough!
There's a retail tool that lets you get a lot more memory below 1MB. 639K (625K free) conventional, 262K upper (177K free).

If you remember seeing how, you'll get a free virtual cookie.

Mmmm, flashbacks of complex sets of AUTOEXEC.BAT & CONFIG.SYS files that we'd swap in and out using batch files to support different memory configurations...