JM> You could install more memory, OS/2 (and amazingly Windows) could 
 JM> not "see" all of it.

It's not that amazing.  All operating systems, OS/2 and DOS-Windows included,
make one or more calls to BIOS routines to query the amount of available
physical RAM.  DOS-Windows calls the EMS and XMS DOS drivers for the
information, but they, in their turn, will have called the BIOS when they
first initialised.

Technically, the calls to supply information about memory over the 16MeB line
are still, even today, classed as extensions to the standard BIOS API.  It's
unsurprising that an AMI BIOS dated 1989, which is around the time when such
machines were becoming popular, might not have been updated yet to include the 
new (at the time) extensions.  It's equally unsurprising that if those
extensions weren't present in the BIOS, operating systems wouldn't "see" any
more than 16MeB of RAM.

 ¯ JdeBP ®

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