INT 21 - HIGHUMM.SYS v1.17+ - IOCTL - GET API ADDRESS
AX = 4402h
BX = handle for device "KSP$UMM"
CX = 0004h
DS:DX -> DWORD to hold entry point
Return: CF set on error
AX = error code (see AH=59h)
CF clear if successful
AX = number of bytes read
Note:   HIGHUMM.SYS is part of "The Last Byte" by Key Software Products

Call HIGHUMM.SYS entry point with:
AH = 00h allocate UMB (same as XMS function 10h) (see INT 2F/AX=4310h)
DX = size in paragraphs
Return: BX = segment number (if successful)
DX = size of requested block/size of largest block
AH = 01h deallocate UMB (same as XMS func 11h) (see INT 2F/AX=4310h)
DX = segment number of UMB
AH = 02h request a bank-switched memory block
DX = size in paragraphs
Return: BX = segment number (if successful)
DX = size of requested block/size of largest block
AH = 03h release a bank-switched memory block
DX = segment number
AH = 04h transfer data to/from high memory
DS:SI -> source
ES:DI -> destination
CX = length in bytes
Note: enables bank-switched memory, does the copy, then disables
bank-switched memory
AH = 05h get a word from bank-switched memory
ES:DI -> word to read
Return: DX = word
AH = 06h put a word to bank-switched memory
ES:DI -> word to write
DX = word
AH = 07h put a byte to bank-switched memory
ES:DI -> byte to write
DL = byte
AH = 08h enable bank-switched memory
DS:SI -> 6-byte status save area
AH = 09h disable bank-switched memory
DS:SI -> 6-byte save area from enable call (AH=08h)
AH = 0Ah assign name to UMB or high bank-switched block
DX = segment number
DS:SI -> 8-byte blank-padded name
AH = 0Bh locate UMB block by name
DS:SI -> 8-byte blank-padded name
Return: BX = segment number (if successful)
DX = size of block
AH = 0Ch locate bank-switched block by name
DS:SI -> 8-byte blank-padded name
Return: BX = segment number (if successful)
DX = size of block
Return: AX = status code
0001h successful
0000h failed
BL = error code
80h not implemented
B0h insufficient memory, smaller block available
B1h insufficient memory, no blocks available
B2h invalid segment number
Note:   only functions 00h and 01h are always available; the remaining
functions are only enabled if the proper commandline switch is given

See also: 214402

214402 - HIGHUMM.SYS v1.17+ - IOCTL - GET API ADDRESS