XT COMPUTERS

Hi René, I guess that would be my specialty. The PC memory map looks like this: C000 - FFFF - Various open areas depending on the individual machine, plus the BIOS B800 - BFFF - Low resolution (CGA or EGA/VGA low res/text) video (if present) B000 - B7FF - Monochrome adapter (if present) A000 - AFFF - High resolution (EGA/VGA) video (if present) 0000 - 9FFF- Base 640K I think what you mean is you'd like to use the high resolution area from A000-AFFF to increase base RAM size. The low resolution area is not contiguous with base RAM so it can't be used to increase base RAM size. The trick is, there is no RAM in this location that you can use to increase the base memory. So, you have to put RAM there somehow (no, video RAM won't work). There are various methods to do this. On a 386 or above, the virtual memory management allows a 386-up memory manager such as EMM386, QEMM386, or 386MAX to map memory into that location. On a 286, you could use various LIM 4.0 compliant expanded memory boards (e.g. Intel AboveBoard Plus) or a wacky device called an ALL Charge Card, along with special software to map memory into the location. On an 8088, you had to use a special card, which was a very simple device containing 64K or more of RAM, along with address selection switches. The card would map RAM into that location, and came with software to extend apparent DOS RAM. Kai