vwestlife
Veteran Member
Yes, it can be done! On an XT-class computer with a color display, you can install a Hercules-compatible display adapter, and instead of using it for monochrome graphics, you can cannibalize nearly all of its 64 KB onboard RAM to use as upper memory for DOS, in which to load device drivers and TSRs using the DEVICEHIGH and LOADHIGH commands normally associated with 386s and newer PCs.
With IBM's PC DOS 6.1 or higher, the UMBHERC.SYS driver takes 60 KB out of the Hercules board's 64 KB video RAM (leaving 4 KB for a monochrome text-only display, if you want to use it) and gives it to you as upper memory. More info, including example CONFIG.SYS commands, at the bottom of this web page:
http://www.robvanderwoude.com/dosmem.html
You can also use UMBMONO.SYS to use the video RAM of a plain text-only MDA card as upper memory, but this only gives you 4 KB of UMBs to work with, barely enough for anything except maybe a small mouse driver (like "CuteMouse" CTMOUSE.EXE).
As that web page mentions, these drivers will also work on a 286 in conjunction with HIMEM.SYS, to give you both HMA and UMB, instead of only HMA without it.
With IBM's PC DOS 6.1 or higher, the UMBHERC.SYS driver takes 60 KB out of the Hercules board's 64 KB video RAM (leaving 4 KB for a monochrome text-only display, if you want to use it) and gives it to you as upper memory. More info, including example CONFIG.SYS commands, at the bottom of this web page:
http://www.robvanderwoude.com/dosmem.html
You can also use UMBMONO.SYS to use the video RAM of a plain text-only MDA card as upper memory, but this only gives you 4 KB of UMBs to work with, barely enough for anything except maybe a small mouse driver (like "CuteMouse" CTMOUSE.EXE).
As that web page mentions, these drivers will also work on a 286 in conjunction with HIMEM.SYS, to give you both HMA and UMB, instead of only HMA without it.