)
Call the XMS driver "Request upper memory block" function with:
AH = 10h
DX = size of block in paragraphs
Return: AX = status
0001h success
BX = segment address of UMB
DX = actual size of block
0000h failure
BL = error code (80h,B0h,B1h) (see #02775)
DX = largest available block
Notes: Upper Memory consists of non-EMS memory between 640K and 1024K
the XMS driver need not implement functions 10h through 12h to be
considered compliant with the standard
under DOS 5+, if CONFIG.SYS contains the line DOS=UMB, then no upper
memory blocks will be available for allocation because all blocks
have been grabbed by MS-DOS while booting
SeeAlso: #02759,#02767,#02785,INT 21/AH=58h"UMB"