> On Jul 9, 2025, at 1:02 PM, Lutalli via Freedos-user > <freedos-user@lists.sourceforge.net> wrote: > > I know very little about UMB, hopefully that's not something too > high-level... Well for now I will write in the HPC forum what I've done to > get to this point, and also ask about UMB. Maybe someone there can get it > working. If I did find a way in the end I will share it here :) > > On Wed, Jul 9, 2025, 18:24 Jerome Shidel via Freedos-user > <freedos-user@lists.sourceforge.net > <mailto:freedos-user@lists.sourceforge.net>> wrote: > > >> On Jul 9, 2025, at 12:22 PM, jer...@shidel.net <mailto:jer...@shidel.net> >> wrote: >> >> Well, if there is usable RAM above 650k, you may be able to get some working >> UMBs. >> > > If there is usable RAM above 640k…
That would be great. :-) As a very general overview. At boot the system will map BIOS extensions (things like VGA BIOS, SCSI ROM, etc) into areas above 640k. If there is actually memory up there, you need to map around the areas that will be in use. For example, the region starting at B800 will be needed for color text mode display. JEMM tries to do this mapping for you automatically. But, sometimes it will need some help. Booting a system without loading anything “high”, then examining the upper memory with a HEX viewer, can help identify regions that are in use. However, there can also be other regions that may get used later or are not able to be used. It can take a bit of trial and error to figure out what regions can be safely used as additional memory. Then once that is accomplished, a little more trial and error to figure out the best order to load programs and drivers making the best use of that memory. :-)
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