INT 21 - Novell NetWare 4.6, Alloy NTNX - RETURN SHELL VERSION
        AH = EAh
        AL = return version environment string
            00h         don't return string
            nonzero     return string in 40-byte buffer pointed to by ES:DI
                Return: buffer filled with three null-terminated entries:
                        major operating system
                        version
                        hardware type
Return: AH = operating system (00h = MSDOS)
        AL = hardware type
            00h IBM PC
            01h Victor 9000
        BH = major shell version
        BL = minor shell version
        CH = (v3.01+) shell type
            00h conventional memory
            01h expanded memory
            02h extended memory
        CL = shell revision number