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Q96522: Regions Scanned by the EMM386.EXE HIGHSCAN Switch

Article: Q96522
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:6.0,6.2,6.21,6.22
Operating System(s): 
Keyword(s): 
Last Modified: 22-NOV-1999

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The information in this article applies to:

- Microsoft MS-DOS operating system versions 6.0, 6.2, 6.21, 6.22 
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SUMMARY
=======

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 device= line.

MORE INFORMATION
================

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.

Additional query words: 6.22 6.00 parameter 6.20

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Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600
Version           : MS-DOS:6.0,6.2,6.21,6.22

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