In order to get Aces over the Pacific (a DOS game) to run on my windows 3.1 386, I had to boot as DOS and then become a bit of a memory expert. I shifted all sorts of stuff to something called himem and other stuff. It needed around 580k of memory to run and the machine only had 640k or something like that.
Sure was a fun game, once I got it going.
I remember Himem.
There was also a company called Quarterdeck that made a memory manager called QEMM.SYS
It would not load under Microsoft DOS. Until I found that if you renamed it to MEMM.sys (replacing th first letter with anything) it would run perfectly. Then I discovered through a binary file search that the string QEMM.SYS was in the COMMAND.COM file- and it would refuse to load it.
Quarterdeck should have OWNED microsoft for that...
Trying to get every available byte of available memory for programs to run was an art. I had multiple config.sys files that I'd use for different purposes. That's one of the uses of 'warm.com' for me. I had written a batch file that would (among other things) bring up a list of configs for specific purposes I'd select the one I wanted, and it would copy it into place then reboot.
I also had a really hairy AT command sequence I tweaked for a long time to get every bit of speed possible out of my modem. Thank God I don't need anything like that anymore.