0x21c unsigned long INITRD_SIZE, size in bytes of ramdisk image
0x220 4 bytes (setup.S)
0x224 unsigned short setup.S heap end pointer
+0x226 unsigned short zero_pad
+0x228 unsigned long cmd_line_ptr
+0x22c unsigned long ramdisk_max
+0x230 16 bytes trampoline
0x290 - 0x2cf EDD_MBR_SIG_BUFFER (edd.S)
0x2d0 - 0x600 E820MAP
0x600 - 0x7ff EDDBUF (edd.S) for disk signature read sector