1. Arctool can create and read a 12 GiB zip file, although it takes more than 4 times as long
It reads the ZIP file (I have done it with 60 GB files), just as fast. What takes the time, is formatting the screen output, so the user can see, and select, the files that are inside the zip file. Overall, much easier to use, but slower.
It's the zip speed I'm concerned with, and that's 4 times as slow. The screen update time is negligible.
2. what are the URLs for the zip and unzip builds that support > 4GiB in OS/2?
I don't know, offhand. I use Arca Noae Package Manager (ANPM) to manage that stuff, so I don't need to do it manually. I expect that they are wherever they post the RPM packages. Whether they will work properly, without all of the other stuff that ANPM (RPM/YUM) installs, I don't care to know.
I also use ANPM to manage that stuff, and the version installed by ANPM is broken. That's why I asked for the URL to a working zip version. I don't care whether it is an rpm, a wpi or a zip, as long as correctly builds a large zip.
4. Several of the other compression tools, e.g., gzip, xz, are intended to compress in place rather than to build a compressed archive.
That doesn't make sense. How can you compress a folder (for example) "in place"? And what good are they, if they don't produce an archive file?
You can't. The default behavior of those utilities is to create a compressed file and delete the original.
Gzip and xz do exactly what ZIP does, they create an archive file out of (a) source file(s).
Not even close. See the Dec 7 reply by David Yeo