0x0000 - 0x03ff : interrupt vector table
0x0400 - 0x04ff : bios data area
0x0500 - 0x05ff : structure pointers
  0x00 : fat
  0x04 : root directory
  0x08 : kernel
  0x0c : file handle array
  0x10 : process array
0x0600 - 0x1fff : not assigned
0x2000 - 0x3fff : memory map
  for each word : 1 page
    0x0000 = free
    0x0001 = unavailable
    0x0002 = kernel
    other = process number

0x4000 - 0x6fff : not assigned
0x7000 - 0x7bff : bootloader scratch
  0x7000 : memory map bios buffer
0x7c00 - 0x7fff : bootloader