RAMdisk-only mod discussed way back at the start by techknight and
Paralel.
So...
This is probably a dumb question, but does someone here actually have one of those CPU upgrades for the LC/LCII that broke the 10MB barrier with onboard memory (
like this one) and if so can they confirm that they actually create "real" RAM instead of requiring a lame hack like running Virtual Memory on a RAM disk? My impression was that the RAMdisk-as-VM thing was something that only applied to upgrades for Macs that originally came with 68000 CPUs. (In which the architecture of the host machine is very messy, the ROMs don't have any built-in 32 bit memory map support, and a software hack, IE "Compact Virtual", was needed to pull off the magic.)
Assuming the LC cards managed to pull off the creation of *real* RAM instead of just a RAMdisk then it would be worth looking into what exactly the drivers for those cards do in order to shuffle the memory map appropriately; things might be *slightly* harder on the Classic II because of the aforementioned issue of the video display being DMA'ed from the EAGLE-controlled RAM instead of being dedicated hardware mapped as a phantom Nubus card, but for the most part the same techniques would apply. (You're just stuck having to do it through the CPU socket instead of via a PDS card.)
Flipping back to those 680x0(*) accelerators for compact Macs in which "excess" RAM above the 4MB mark can *only* be used as a RAMdisk I have to admit I'm curious how that's actually accomplished, IE, is the RAM a linear block so far as the CPU is concerned but using the MMU to shuffle together a "real" 32 bit linear address space for MacOS a bridge too far given the other limitations of a 68000-targeted host machine, or do those cards have a paging unit built onto them that presents all RAM above the limit as "pages" or "sectors"?
(Edit: Changed to "680x0" because... I may be wrong, but I could sort of swear that there might have been MMU-less *68020* accellerators that also included extra RAM that could only be used for a RAMdisk? It would seem a card like that would *have* to do some interesting tricks with page-flipping in order to let it be used at all, with the magic crammed into the RAMDISK driver.)