title: Memory map shows more RAM than physically available
body: <p>I am working on a small x86 kernel.  I am accessing and attempting to read the memory map that GRUB provides in the multiboot header.  I have an Intel i3 cpu and 4 GiB of RAM.  While running on this machine, I am reading the following memory map:</p>
  
  <pre><code> --Base Address--          --Length--      --Type--
  
  0x0000000000000000     0x000000000009d000     0x1
  0x000000000009d000     0x0000000000003000     0x2
  0x00000000000e0000     0x0000000000020000     0x2
  0x0000000000100000     0x00000000bb53f000     0x1
  0x00000000bb63f000     0x0000000000080000     0x2
  0x00000000bb6bf000     0x0000000000100000     0x4
  0x00000000bb7bf000     0x0000000000040000     0x3
  0x00000000bb7ff000     0x0000000000001000     0x1
  0x00000000bb800000     0x0000000004800000     0x2
  0x00000000e0000000     0x0000000010000000     0x2
  0x00000000feb00000     0x0000000000004000     0x2
  0x00000000fec00000     0x0000000000001000     0x2
  0x00000000fed10000     0x0000000000004000     0x2
  0x00000000fed18000     0x0000000000002000     0x2
  0x00000000fed1b000     0x0000000000005000     0x2
  0x00000000fee00000     0x0000000000001000     0x2
  0x00000000ffe80000     0x0000000000180000     0x2
  0x0000000100000000     0x0000000038000000     0x1
  </code></pre>
  
  <p>When I total up the available memory areas, I get...</p>
  
  <p><strong>0x1 (Available)</strong>  - 3893.8 MiB</p>
  
  <p>Which seems about right, leaving the last 200ish MiB reserved for other devices.
  The only problem is the total of the other memory types:</p>
  
  <p><strong>0x2, 0x3, 0x4</strong> - 331.5 MiB</p>
  
  <p>Putting my total amount of RAM at 4225.3 MiB or <strong>a little over 4.1 GiB</strong>, which leads me to my questions:</p>
  
  <ol>
  <li><p>Why am I totaling more than 4GiB of RAM when I only have 4GiB installed?</p></li>
  <li><p>Why is the last base address in the memory map 0x0000000100000000?  With only 4GiB of RAM, 32 bits should be the max address size needed to address all of it.  Am I misunderstanding something here?</p></li>
  </ol>