Int 31 Fn FF1B  P - Causeway - "lockmem" - Lock Region Of Memory           [E]

   AX = FF1Bh
   BX:CX = starting linear address
   SI:DI = size of region in bytes

Return: CF clear if successful
   CF set on error
Desc:  prevent memory from being swapped out by the virtual memory manager

Note:  locks are applied on 4K page boundaries, so memory above and below
     the specified region may be locked as well

See Also: AX=FF1Ch,AX=FF1Dh