15.2. E820 Assumptions and Limitations¶
The platform boot firmware returns address ranges describing baseboard memory.
The platform boot firmware does not return a range description for the memory mapping of PCI devices, ISA Option ROMs, and ISA Plug and Play cards because the OS has mechanisms available to detect them.
The platform boot firmware returns chip set-defined address holes that are not being used by devices as reserved.
Address ranges defined for baseboard memory-mapped I/O devices, such as APICs, are returned as reserved.
All occurrences of the system platform boot firmware are mapped as reserved, including the areas below 1 MB, at 16 MB (if present), and at end of the 4-GB address space.
Standard PC address ranges are not reported. For example, video memory at A0000 to BFFFF physical addresses are not described by this function. The range from E0000 to EFFFF is specific to the baseboard and is reported as it applies to that baseboard.
All of lower memory is reported as normal memory. The OS must handle standard RAM locations that are reserved for specific uses, such as the interrupt vector table (0:0) and the platform boot firmware data area (40:0).