ID Number: Q39370
5.00 5.10a 6.00 6.00a 6.00b
MS-DOS
Summary:
When a 80286 or higher processor is in real mode, addressing is done
using a 16-bit segment and 16-bit offset. Therefore, it is only
possible to address up to 1 megabyte of memory. To address memory
above 1 meg under DOS, you have to put the processor into protected
mode by using IBM ROM BIOS Interupt 15 Function 89h. Addressing will
be done using a selector into a descriptor table.
For more information about this interrupt, call IBM hardware support,
(800) 426-2468. If ROM BIOS routines are not operating as expected,
you may need to contact the company that supplied the BIOS in your
particular machine.
For more information about protected mode, selectors and descriptor
tables, see the Intel guides for the 80286, 80386, or 80486 or
"Microsoft's 80386/80486 Programming Guide".