Function 5803h Set Upper-Memory Link

mov bx, LinkFlag ;1= link, 0 = unlink

mov ax, 5803h ;Set Upper-Memory Link

int 21h

jc error_handler ;carry clear means error

Set Upper-Memory Link (Function 5803h) links or unlinks the upper memory area. When this area is linked, a program can allocate memory from it.

Parameters

LinkFlag

Specifies whether to link or unlink the upper memory area. If this parameter is 01h, the function links the area; if the parameter is 00h, the function unlinks the area.

Return Value

If the function is successful, the carry flag is clear. Otherwise, the carry flag is set and the AX register contains an error value, which may be one of the following:

Value

Name

0001h	ERROR_INVALID_FUNCTION.
0007h	ERROR_ARENA_TRASHED

Comments

The function returns 0001h (ERROR_INVALID_FUNCTION) if MS-DOS has been loaded without the command dos=umb having been specified in the CONFIG.SYS file.

For more information about upper memory blocks and memory allocation, see Chapter 5, “Program Management.”