In reference to bit 0 of the flags parameter in the Multiboot
information structure, if the bootloader in question uses older
BIOS interfaces, or the newest ones are not available (see
description about bit 6), then a maximum of either 15 or 63 megabytes of
memory may be reported. It is highly recommended that boot
loaders perform a thorough memory probe.
In reference to bit 1 of the flags parameter in the Multiboot
information structure, it is recognized that determination of which
BIOS drive maps to which device driver in an operating system is
non-trivial, at best. Many kludges have been made to various operating
systems instead of solving this problem, most of them breaking under
many conditions. To encourage the use of general-purpose solutions to
this problem, there are 2 BIOS device mapping techniques
(see BIOS device mapping techniques).
In reference to bit 6 of the flags parameter in the Multiboot
information structure, it is important to note that the data structure
used there (starting with BaseAddrLow) is the data returned by
the INT 15h, AX=E820h -- Query System Address Map call. See See Query System Address Map, for more information. The interface here is meant to allow a
boot loader to work unmodified with any reasonable extensions of the
BIOS interface, passing along any extra data to be interpreted by
the operating system as desired.