请问一个物理内存的问题

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本身我的机器是有12G内存=12288M

可是系统起来后，使用cat meminfo 看到的totalram只有大概11511M。我想请问那700多M哪里去了。。

在开机的日志中，我找到了物理映射的那部分，把usable部分加起来也就只有11924M。

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~ # free
                       total         used               free       shared      buffers
  Mem:      11831768     11149472       682296            0       112140
Swap:            0            0            0
Total:     11831768     11149472       682296
这个是free后看到的内存。只有11831768KB

下面这个是iomem后：/proc # cat iomem
00000000-0000ffff : reserved
00010000-00081bff : System RAM
00081c00-0008ffff : RAM buffer
000e0000-000fffff : reserved
00100000-7526ffff : System RAM
  01000000-0151aeef : Kernel code
  0151aef0-01805697 : Kernel data
  018aa000-019455b3 : Kernel bss
  02000000-09ffffff : Crash kernel
75270000-77ffffff : RAM buffer
7e6a9000-7e7b5fff : ACPI Non-volatile Storage
7e7b6000-7f3b9fff : reserved
7f3ba000-7f433fff : ACPI Tables
7f434000-7f4b1fff : reserved
7f4b2000-7f4b2fff : System RAM
7f4b3000-7f4b3fff : ACPI Non-volatile Storage
7f4b4000-7f4b9fff : reserved
7f4ba000-7f4c1fff : ACPI Non-volatile Storage
7f4c2000-7f4e9fff : reserved
7f4ea000-7f56ffff : ACPI Non-volatile Storage
7f570000-7f62efff : System RAM
7f62f000-7f6fffff : RAM buffer
7f700000-7f7fffff : System RAM
7f800000-7fffffff : RAM buffer
80000000-8fffffff : PCI MMCONFIG 0 [00-ff]
  80000000-8fffffff : reserved
fa000000-faffffff : PCI Bus 0000:07
  fa000000-faffffff : 0000:07:00.0
fb000000-fb8fffff : PCI Bus 0000:07
  fb000000-fb7fffff : 0000:07:00.0
  fb800000-fb80ffff : 0000:07:00.0
  fb810000-fb813fff : 0000:07:00.0
fb900000-fbbfffff : PCI Bus 0000:02
  fb900000-fb97ffff : 0000:02:00.3
    fb900000-fb97ffff : igb_uio
  fb980000-fb9fffff : 0000:02:00.2
    fb980000-fb9fffff : igb_uio
  fba00000-fba7ffff : 0000:02:00.1
    fba00000-fba7ffff : igb_uio
  fba80000-fbafffff : 0000:02:00.0
    fba80000-fbafffff : igb_uio
  fbb00000-fbb03fff : 0000:02:00.3
    fbb00000-fbb03fff : igb_uio
  fbb04000-fbb07fff : 0000:02:00.2
    fbb04000-fbb07fff : igb_uio
  fbb08000-fbb0bfff : 0000:02:00.1
    fbb08000-fbb0bfff : igb_uio
  fbb0c000-fbb0ffff : 0000:02:00.0
    fbb0c000-fbb0ffff : igb_uio
fbc00000-fbdfffff : PCI Bus 0000:01
  fbc00000-fbcfffff : 0000:01:00.0
  fbd00000-fbd0ffff : 0000:01:00.0
  fbd10000-fbd1ffff : 0000:01:00.0
  fbd20000-fbd2ffff : 0000:01:00.0
  fbd30000-fbd3ffff : 0000:01:00.0
fbe00000-fbefffff : PCI Bus 0000:05
  fbe00000-fbe1ffff : 0000:05:00.1
    fbe00000-fbe1ffff : igb
  fbe20000-fbe3ffff : 0000:05:00.0
    fbe20000-fbe3ffff : igb
  fbe40000-fbe43fff : 0000:05:00.1
    fbe40000-fbe43fff : igb
  fbe44000-fbe47fff : 0000:05:00.0
    fbe44000-fbe47fff : igb
fbf00000-fbf007ff : 0000:00:1f.2
  fbf00000-fbf007ff : ahci
fbf01000-fbf013ff : 0000:00:1d.0
  fbf01000-fbf013ff : ehci_hcd
fbf02000-fbf023ff : 0000:00:1a.0
  fbf02000-fbf023ff : ehci_hcd
fbf06000-fbf06fff : 0000:00:05.4
fc000000-fcffffff : pnp 00:01
fd000000-fdffffff : pnp 00:01
fe000000-fe00ffff : reserved
feb00000-febfffff : pnp 00:01
fec00000-fec00fff : IOAPIC 0
fec01000-fec01fff : IOAPIC 1
fed00000-fed003ff : HPET 0
fed08000-fed08fff : pnp 00:0a
fed1c000-fed1ffff : reserved
  fed1c000-fed1ffff : pnp 00:0a
fed45000-fedfffff : pnp 00:01
fee00000-fee00fff : Local APIC
ff000000-ffffffff : reserved
  ff000000-ffffffff : pnp 00:0a
100000000-3716fffff : System RAM
371700000-37fffffff : reserved
3c2000000000-3c2fffffffff : 0000:00:03.0
  3c2000000000-3c2fffffffff : config_ntb
3c3000000000-3c37ffffffff : 0000:00:03.0
  3c3000000000-3c37ffffffff : config_ntb
3c3800000000-3c38000fffff : PCI Bus 0000:05
  3c3800000000-3c380001ffff : 0000:05:00.0
  3c3800020000-3c380003ffff : 0000:05:00.0
  3c3800040000-3c380005ffff : 0000:05:00.1
  3c3800060000-3c380007ffff : 0000:05:00.1
3c3800100000-3c380010ffff : 0000:00:03.0
  3c3800100000-3c380010ffff : config_ntb
3c3ffff00000-3c3ffff03fff : 0000:00:04.7
  3c3ffff00000-3c3ffff03fff : dmauio
3c3ffff04000-3c3ffff07fff : 0000:00:04.6
  3c3ffff04000-3c3ffff07fff : dmauio
3c3ffff08000-3c3ffff0bfff : 0000:00:04.5
  3c3ffff08000-3c3ffff0bfff : dmauio
3c3ffff0c000-3c3ffff0ffff : 0000:00:04.4
  3c3ffff0c000-3c3ffff0ffff : dmauio
3c3ffff10000-3c3ffff13fff : 0000:00:04.3
  3c3ffff10000-3c3ffff13fff : dmauio
3c3ffff14000-3c3ffff17fff : 0000:00:04.2
  3c3ffff14000-3c3ffff17fff : dmauio
3c3ffff18000-3c3ffff1bfff : 0000:00:04.1
  3c3ffff18000-3c3ffff1bfff : dmauio
3c3ffff1c000-3c3ffff1ffff : 0000:00:04.0
  3c3ffff1c000-3c3ffff1ffff : dmauio
3c3ffff20000-3c3ffff200ff : 0000:00:1f.3
/proc #

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这个是启动后是map信息：
[    0.000000] BIOS-provided physical RAM map:
[    0.000000]  BIOS-e820: 0000000000000000 - 0000000000081c00 (usable)
[    0.000000]  BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
[    0.000000]  BIOS-e820: 0000000000100000 - 0000000077c7d000 (usable)
[    0.000000]  BIOS-e820: 000000007e6a9000 - 000000007e7b6000 (ACPI NVS)
[    0.000000]  BIOS-e820: 000000007e7b6000 - 000000007f3ba000 (reserved)
[    0.000000]  BIOS-e820: 000000007f3ba000 - 000000007f434000 (ACPI data)
[    0.000000]  BIOS-e820: 000000007f434000 - 000000007f4b2000 (reserved)
[    0.000000]  BIOS-e820: 000000007f4b2000 - 000000007f4b3000 (usable)
[    0.000000]  BIOS-e820: 000000007f4b3000 - 000000007f4b4000 (ACPI NVS)
[    0.000000]  BIOS-e820: 000000007f4b4000 - 000000007f4ba000 (reserved)
[    0.000000]  BIOS-e820: 000000007f4ba000 - 000000007f4c2000 (ACPI NVS)
[    0.000000]  BIOS-e820: 000000007f4c2000 - 000000007f4ea000 (reserved)
[    0.000000]  BIOS-e820: 000000007f4ea000 - 000000007f570000 (ACPI NVS)
[    0.000000]  BIOS-e820: 000000007f570000 - 000000007f62f000 (usable)
[    0.000000]  BIOS-e820: 000000007f700000 - 000000007f800000 (usable)
[    0.000000]  BIOS-e820: 0000000080000000 - 0000000090000000 (reserved)
[    0.000000]  BIOS-e820: 00000000fe000000 - 00000000fe010000 (reserved)
[    0.000000]  BIOS-e820: 00000000fed1c000 - 00000000fed20000 (reserved)
[    0.000000]  BIOS-e820: 00000000ff000000 - 0000000100000000 (reserved)
[    0.000000]  BIOS-e820: 0000000100000000 - 0000000371700000 (usable)
[    0.000000]  BIOS-e820: 0000000371700000 - 000000037df00000 (reserved)
[    0.000000]  BIOS-e820: 000000037df00000 - 0000000380000000 (reserved)