道理我都懂，可是为什么内存 4G 只能识别 3G？？

[tntsec]

cat /etc/redhat-release
CentOS release 6.6 (Final)Markdown

free -m
total used free shared buffers cached
Mem: 3129

uname -a
Linux gov.jp 2.6.32-504.el6.x86_64 #1 SMP Wed Oct 15 04:27:16 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

图片不会传，看贴吧里的图片吧
http://tieba.baidu.com/p/4107251680

[yxaaa123]

1g 给显卡了

[wuxqing]

用 dmesg | grep reserved
看看是不是被系统预留了

[VYSE]

咋还有说 32 位的，人家就是 x86_64 ，楼主去 bios 里看看可用内存就知道。例如 INTEL 945 之前的 memory-mapped I/O 与物理内存冲突干脆直接 bios 强行封印物理内存，有的封印多有的封印少。

[gamexg]

楼主的是 64 位系统...

[Ouyangan]

核显占用了吧

[realpg]

换主板。
你这主板就这样了，主板自身最高支持内存 4G ，且映射进系统时候会屏蔽不少内存。
G31 这玩意还用着呢……

[chevalier]

@tntsec 不到 1G ， Windows 下面我看大概是 700M 左右

[clink8001]

操作系统也是软件，他的存在本身是要占用一部分内存的，剩下的才是可用的内存。

[yksoft1]

其实在某些笔记本上还可能小于 3GB

[chenai00]

真的是汪汪姐？😀😀😀

[tntsec]

@wuxqing dmesg | grep reserved
BIOS-e820: 000000000009f800 - 00000000000a0000 (reserved)
BIOS-e820: 00000000000e6000 - 0000000000100000 (reserved)
BIOS-e820: 00000000cf6f0000 - 00000000cf700000 (reserved)
BIOS-e820: 00000000fed00000 - 00000000fed00400 (reserved)
BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
BIOS-e820: 00000000ff380000 - 0000000100000000 (reserved)
e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved)
e820 update range: 0000000000000000 - 0000000000001000 (usable) ==> (reserved)
#4 [000009f800 - 0000100000] BIOS reserved ==> [000009f800 - 0000100000]
DMA zone: 103 pages reserved
Memory: 3182444k/3398336k available (5336k kernel code, 452k absent, 215440k reserved, 7016k data, 1292k init)
PCI: MCFG area at e0000000 reserved in ACPI motherboard resources
system 00:01: [mem 0xfed14000-0xfed19fff] has been reserved
system 00:07: [io 0x04d0-0x04d1] has been reserved
system 00:07: [io 0x0800-0x087f] has been reserved
system 00:07: [io 0x0480-0x04bf] has been reserved
system 00:07: [io 0x0900-0x090f] has been reserved
system 00:07: [mem 0xfed1c000-0xfed1ffff] has been reserved
system 00:07: [mem 0xfed20000-0xfed8ffff] has been reserved
system 00:09: [mem 0xffc00000-0xfff7ffff] has been reserved
system 00:0a: [mem 0xfec00000-0xfec00fff] could not be reserved
system 00:0a: [mem 0xfee00000-0xfee00fff] has been reserved
system 00:0c: [io 0x0280-0x028f] has been reserved
system 00:0c: [io 0x0290-0x029f] has been reserved
system 00:0d: [mem 0xe0000000-0xefffffff] has been reserved
system 00:0e: [mem 0x00000000-0x0009ffff] could not be reserved
system 00:0e: [mem 0x000e0000-0x000fffff] could not be reserved
system 00:0e: [mem 0x00100000-0xcf6fffff] could not be reserved

[tntsec]

@xierch 哈哈哈，看来你懂这个梗~

[javaluo]

@tntsec however 节点？

[tntsec]

@javaluo 啥？不懂

[salmon5]

http://serverfault.com/questions/81126/linux-x86-64-reports-3-2g-of-memory-instead-of-4g

Go in the BIOS. There should be a Memory Remap Feature option (probably in the Advanced menu) which is disabled by default. Enable it and try again.

[tntsec]

@salmon5
Mem: 3823

OK ！！

他还感谢我，啊哈哈

You are welcome :) Thank you for showing us how to resolve that issue.

[lyz1990]

道理我都懂啊，可是我 16G 的内存在 64 位 Ubuntu 上也是显示的 15.4G 　啊