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If bit 6 in the flags word is set, then the mmap_* fields are valid, and indicate the address and length of a buffer containing a memory map of the machine provided by the BIOS. mmap_addr is the address, and mmap_length is the total size of the buffer. The buffer consists of one or more of the following size/structure pairs (size is really used for skipping to the next pair):

[tt]
+-------------------+
-4 | size |
+-------------------+
0 | base_addr_low |
4 | base_addr_high |
8 | length_low |
12 | length_high |
16 | type |
+-------------------+
[/tt]

where size is the size of the associated structure in bytes, which can be greater than the minimum of 20 bytes. base_addr_low is the lower 32 bits of the starting address, and base_addr_high is the upper 32 bits, for a total of a 64-bit starting address. length_low is the lower 32 bits of the size of the memory region in bytes, and length_high is the upper 32 bits, for a total of a 64-bit length. type is the variety of address range represented, where a value of 1 indicates available RAM, and all other values currently indicated a reserved area.

durand wrote: If you are only running a 32 bit machine and you have less than 4GB of memory, then it's kind of safe to ignore the high bits. So, your memory range will start at base_low and will be length_low bytes long.

Dragon_Hilord wrote: I'm having a hard time finding C code for the purpose.

hm. not quite. What about a region starting at 0x0000,0001,FF00,0000 and ending at 0x0000,0001,FFFF,FFFF, for instance ? ignoring the highest bits will lead to errors if those bits aren't 0. If your OS doesn't support memory above 4GB, it should rather ignore regions with "base.high>0" and truncate regions with "limit.high>0" to limit=0x0000,0000,FFFF,FFFF, imho.