INT 68 - APPC/PC - GET ALLOCATE
        AH = 03h subfn 2800h
        DS:DX -> control block (see below)
Return: control block updated

Format of control block:
Offset  Size    Description
 00h 12 BYTEs   reserved
 0Ch    WORD    2800h (verb "Get ALLOCATE")
 0Eh  6 BYTEs   00h
 14h    DWORD   (big-endian) return code (see AH=01h/SF=1B00h)
 18h    WORD    00h
 1Ah  8 BYTEs   (big-endian) logical unit ID
 22h    BYTE    type (00h dequeue, 01h test)
 23h    DWORD   pointer to CREATE_TP record

.