Microsoft KB Archive/63862

= LAN Adapter, 16-Bit VGA Adapter Shared Memory Conflict =

Article ID: 63862

Article Last Modified on 9/30/2003

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APPLIES TO


 * Microsoft LAN Manager 2.0 Standard Edition
 * Microsoft LAN Manager 2.1 Standard Edition
 * Microsoft LAN Manager 2.1a
 * Microsoft LAN Manager 2.2 Standard Edition

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This article was previously published under Q63862



SYMPTOMS
Conflicts in memory addressing may occur when shared-memory architecture LAN adapters (for example, the Western Digital WD8003E) are used with 16- bit VGA adapters.

The LAN adapter software does not load properly: either the MAC driver refuses to load, NetBind fails, or LAN operation is severely impaired.



CAUSE
This conflict exists because some VGA adapters operating in 16-bit mode use two 128K memory segments (0xA0000 - 0xBFFFF video RAM, 0xC0000 - 0xDFFFF ROM). If the VGA adapter does this, it blocks out the memory regions that many LAN adapters need. Under MS-DOS, LAN adapters with &quot;Autoswitch&quot; may function properly; however, this Autoswitch feature does not work with OS/2 and the LAN adapters will probably fail.



RESOLUTION
There are four possible solutions to this problem:


 * 1) Run the LAN adapter in a nonshared-memory mode. Some LAN adapters (for example, the 3Com 3C503 adapter) are capable of running in either a DMA, Programmed I/O, or shared-memory mode.
 * 2) In some computers, it may be possible to base the LAN adapter's shared- memory region at 0xE0000 (this region is used in IBM equipment for BASIC ROMs, but should be free in Compaqs and most compatibles). A determination of whether or not this region is free can be made under MS-DOS using DEBUG or a memory-analysis tool.
 * 3) Set the VGA adapter to run in 8-bit BIOS mode (on some VGA adapters this can be done independently of the memory access mode). This will impact the performance of MS-DOS, but not that of OS/2 or Windows. On VGA boards where the memory access mode cannot be set independently of the BIOS mode, this will severely impact performance in all operations.
 * 4) Set the VGA adapter to run in &quot;Autoswitch&quot; mode. This will work only in MS-DOS. It may not work under Windows, and will not work under OS/2.

For more information on this topic, consult the LAN adapter manufacturer.

Additional query words: 1.00 2.00 2.10 2.10a 2.20

Keywords: KB63862

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