Why AutoCAD 386 Doesn't Work with Windows NT

• Microsoft Windows NT operating system version 3.1
• Microsoft Windows NT Advanced Server version 3.1
• Microsoft Windows NT Workstation versions 3.5 and 3.51
• Microsoft Windows NT Server versions 3.5 and 3.51
• Microsoft Windows NT Server version 4.0
• Microsoft Windows NT Workstation version 4.0

SUMMARY

AutoCAD 386 release 11 and 12 do not run with Windows NT because AutoCAD 386 requires DPMI version 1.0 and Windows NT supports version 0.9. When you try to run AutoCAD 386 in a virtual machine, you receive the following Pharlap error message:

   The 386 chip is currently executing in virtual 8086 mode under the
   control of another program. You must turn off this other program in
   order to use 386 DOS-Extender to run in protected mode.

MORE INFORMATION

The AutoCAD memory model requires the ability to map a block of a virtual machine's conventional memory (below 640K) into one or more of its protected mode segments.

NOTE: The same conventional memory block is mapped by AutoCAD into multiple protected mode segments; therefore, any extensions must not assume a 1-to-1 mapping between a particular conventional memory block and a particular segment.

For AutoCAD to run from the Windows NT MS-DOS command prompt:

• Microsoft would have to implement DPMI 1.0 call 0509 (Map Conventional Memory) in the NT DPMI server. 386|DOS-Extender detects this functionality by making DPMI call 0401 (Get DPMI Capabilities) and checking if bit 3 is set in AX. This is how AutoCAD runs under OS/2 2.0.

  -or-

• An NT driver would need to be written with the same functionality that the PHARLAP.386 device driver provides when it is loaded under Windows 3.1. This functionality allows 386|DOS-Extender to remap arbitrary linear regions be reading and writing PTEs for pages that are locked in memory. It also requires that DPMI calls 0600 and 0601 actually lock pages into memory so they don't move after they are remapped. 386|DOS-Extender detects this capability by making DPMI call 0A00 with DS:ESI pointing to the string "PHARLAP.LINEAR_REMAP." If the capability is present, it returns an entry point that 386|DOS-Extender can call to remap linear regions.