Why would you need >512K RAM?
I thought I was completely bada** when I “sold” a small program to Quadram, an early PC expansion board manufacturer, for 192k of RAM to fully populate my Quadboard (4-function expansion board with RAM, parallel and serial ports, and clock). It took my system from 128K to 320K of RAM, which was a *lot* at the time (late-’82 or early-’83).