Multiboot Specification

Node: Notes on PC, Next: BIOS device mapping techniques, Up: Examples

### Notes on PC

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.