SUMMARY

Loading one part of the 10net redirector (10NET.EXE) high into the upper memory blocks (UMBs) causes the Unisys 386 workstation to hang. A cold boot is required to restart the workstation.

This is NOT a problem with MS-DOS version 5.0; this is a problem with the DCA 10net software. There are two problems with the 10NET.EXE file:

• 10NET.EXE moves its code to 64K above the current code segment without checking the top of memory value in the program segment prefix. If it is loaded into a UMB, results may be unpredictable.
• 10NET.EXE's header has a nonzero initial system stack (SS) value and a zero initial stack pointer (SP) value. When DOS pushes the return address on the user stack to transfer control, it actually goes into the 64K region above the SS. This mode of control transfer may lead to unpredictable results. In the case of loading into UMBs, it could be pointing to ROM or an unmapped region.