Regions Scanned by the EMM386.EXE HIGHSCAN Switch (96522)
The information in this article applies to:
• Microsoft MS-DOS operating system 6.0
• Microsoft MS-DOS operating system 6.2
• Microsoft MS-DOS operating system 6.21
• Microsoft MS-DOS operating system 6.22
This article was previously published under Q96522
The EMM386.EXE version 4.45 and 4.48 HIGHSCAN switch allows EMM386.EXE to
map expanded memory pages or upper memory blocks (UMBs) over portions of
the upper memory area (UMA) used by system read-only memory (ROM).
Choosing "Yes" in response to the MemMaker prompt "Scan the upper memory
area aggressively?" causes MemMaker to add HIGHSCAN to the EMM386.EXE
If you use the HIGHSCAN switch on the DEVICE=C:\DOS\EMM386.EXE line in the
CONFIG.SYS file, EMM386.EXE examines the system ROM area starting at memory
location F000:0000. If EMM386.EXE determines that ROM is duplicated between
F000h-F7FFh and F800h-FFFFh, EMM386.EXE uses the F000h-F7FFh region for
expanded memory page mapping or UMB memory. (This adds up to 32 kilobytes
to the UMA.
On Micro Channel (MCA) systems with ROM BASIC (for example, IBM PS/2
systems), the HIGHSCAN switch allows EMM386.EXE to map expanded memory or
UMB memory over the ROM BASIC code in the system ROM. Typically this is the
region from F600 to FDFF.
Note: On some systems, EMM386.EXE uses the ROM area and the system does not
operate correctly. The symptoms of this condition vary. For example, the
system may stop responding (hang) or appear to operate normally until you
use a floppy disk drive. Because of these potential problems, HIGHSCAN is
not used by default.
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