Using the /HIGH and /DS LINK Options

The information in this article applies to:

• Microsoft LINK for MS-DOS, versions 2.x, 3.x, 4.x, 5.0x, 5.1x, 5.2, 5.3x, and 5.5

SUMMARY

The Microsoft LINK /HIGH option instructs the loader to place to program into RAM at the highest possible address. However, the Program Segment Prefix (PSP) is loaded into low memory. When the LINK command line does not include the /HIGH option, the entire program is loaded into the lowest possible address in the first available block of RAM.

The LINK /DS[ALLOCATE] option relocates each address in DGROUP such that the last byte in the segment has offset FFFFh.

The /DS and /HIGH options are not recommended for use with applications developed in a high-level language. These switches are provided for use with a real-mode assembly-language application.

MORE INFORMATION

When the LINK command line specifies the /HIGH option, the application owns all memory between its segments (which are loaded at the highest possible address) and its PSP (which is loaded into low memory). Therefore, the application cannot dynamically allocate and free memory nor can any other program be loaded into memory.

The /HIGH switch provides room for the application stack or heap to grow downward without colliding with any other program data, if the stack or heap is the first segment in the memory map.

The start-up code for the Microsoft high-level language libraries is not compatible with the /HIGH option. The libraries automatically specify the /DOSSEG option which loads program segments into low memory. The libraries also require dynamic memory allocation. Even though it is possible to use the /HIGH option with custom start-up code, many of the run-time library functions that require dynamic memory allocation would not be available.

Early versions of Microsoft FORTRAN and Microsoft Pascal generate code that must be linked with the /DS option specified. Because the /HIGH option is often used in conjunction with /DS, Microsoft LINK continues to support these options.