Believe it or not in 2016 I came across updating some aging x86 hardware, and it did not want to boot from our usual so2stick.sh T2 USB pen drive disk images. After some research and debugging it turned out syslinux has the answer:
On these BIOSes, you’re generally stuck booting them in USB-ZIP mode.
A standard zipdrive (both the 100 MB and the 250 MB varieties) have a “geometry” of 64 heads, 32 sectors, and are partitioned devices with a single partition 4 (unlike most other media of this type which uses partition 1.) The 100 MB variety has 96 cylinders, and the 250 MB variety has 239 cylinders;
And this stupid hack indeed works, sigh. PC BIOS programmers, a very special kind of bread, … :-/