Was looking at this PC card recently: https://texelec.com/product/lo-tech-1mb-ram/
Got me wondering - is there any reason the same couldn't be done for the Lisa? I realize that product's using SRAM and not DRAM but apparently you can still get 4Mbit DRAM new. Would be cool to make modern-day RAM boards to get people up to 2MB or beyond for not a whole lot.
Sounds wonderful. SRAM would make the Lisa a tiny bit faster since refresh won't be needed, maybe remove some wait states but yes, for LOS/Xenix/Unix, the limit is 2MB. James MacPhail has posted a way to modify the RAM board to get 4MB:
https://lisalist2.com/index.php/topic,29.0.html but this will only work with MacWorks - not sure what happens if you boot LOS on such a machine, whether it will ignore the extra RAM or if it will fail. If it fails, perhaps some sort of switch with a cable out the back will do the trick to disable the extra 2MB.
Not sure what will happen to the DRAM refresh cycles and how they'd interact, I suspect (but likely am wrong) that all they'll do is read all the RAM every so many cycles, and I suspect this is tied in to the video refresh cycles, so not sure if you'd need to do something to block that cycle from reaching SRAM, or signal something back for completion, etc.