Solving the "Insufficient Memory to Run" Situation

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SUMMARY

Each task under Windows requires a data structure allocated below 1 megabyte (MB) called the Task Data Base (TDB). Under the debug version of Windows, failure of a TDB's allocation shows up as:

   t Kernel: GlobalAlloc(200) failed for ????

The most common cause of low conventional memory is fixed allocations made on behalf of a dynamic-link library (DLL). Fixed allocations should be used only for code and data touched at interrupt time. All other allocations should be made with the moveable attribute.

MORE INFORMATION

The Windows heap consists of all conventional and XMS memory available after WIN.COM and WIN386.EXE/DOSX.EXE are loaded by MS-DOS. These two physically separate blocks are combined into a single linear address space to make up the global heap.

Windows allocates fixed objects with a bottom up/first fit algorithm. As more fixed objects are allocated from the heap, conventional memory gets pinched. Eventually, even a small allocation for the TDB fails resulting in LoadModule returning 0 (zero).

The HEAPWALK.EXE utility provides a view onto the global heap to determine what is using up conventional memory. The Sort Address menu item sorts the main heap with lower addresses at the top of the list. Any object with an address of 9FFFF or below is in conventional memory. An object with an "F" set in the FLG column is fixed. Any fixed object owned by an application or its dependent dynamic-link libraries that is not a TDB (TYPE Task in HEAPWALK) should be considered suspect.

The module definition (.DEF) file should mark CODE MOVEABLE DISCARDABLE and DATA MOVEABLE. Any allocations should contain the GMEM_MOVEABLE attribute. The EXEHDR.EXE utility can be used to indentify modules that use the fixed attribute for their code or data segments. Segments without the <moveable> attribute in the "flags" column of EXEHDR's output are fixed.