怎么会这样：
$ sudo dmidecode -t memory
[sudo] password for dims:
# dmidecode 2.12
SMBIOS 2.6 present.
Handle 0x0008, DMI type 6, 12 bytes
Memory Module Information
Socket Designation: DIMM0
Bank Connections: 0 1
Current Speed: Unknown
Type: DIMM SDRAM
Installed Size: 2048 MB (Double-bank Connection)
Enabled Size: 2048 MB (Double-bank Connection)
Error Status: OK
Handle 0x0009, DMI type 6, 12 bytes
Memory Module Information
Socket Designation: DIMM1
Bank Connections: 2 3
Current Speed: Unknown
Type: DIMM SDRAM
Installed Size: 4096 MB (Double-bank Connection)
Enabled Size: 4096 MB (Double-bank Connection)
Error Status: OK
Handle 0x000A, DMI type 6, 12 bytes
Memory Module Information
Socket Designation: DIMM2
Bank Connections: 4 5
Current Speed: Unknown
Type: DIMM SDRAM
Installed Size: 2048 MB (Double-bank Connection)
Enabled Size: 2048 MB (Double-bank Connection)
Error Status: OK
Handle 0x000B, DMI type 6, 12 bytes
Memory Module Information
Socket Designation: DIMM3
Bank Connections: 6 7
Current Speed: Unknown
Type: DIMM SDRAM
Installed Size: 4096 MB (Double-bank Connection)
Enabled Size: 4096 MB (Double-bank Connection)
Error Status: OK
Handle 0x0030, DMI type 16, 15 bytes
Physical Memory Array
Location: System Board Or Motherboard
Use: System Memory
Error Correction Type: None
Maximum Capacity: 16 GB
Error Information Handle: Not Provided
Number Of Devices: 4
Handle 0x0032, DMI type 17, 28 bytes
Memory Device
Array Handle: 0x0030
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 2048 MB
Form Factor: DIMM
Set: None
Locator: DIMM0
Bank Locator: BANK0
Type: DDR
Type Detail: Synchronous
Speed: 1333 MHz
Manufacturer: Manufacturer0
Serial Number: SerNum0
Asset Tag: AssetTagNum0
Part Number: PartNum0
Rank: Unknown
Handle 0x0034, DMI type 17, 28 bytes
Memory Device
Array Handle: 0x0030
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 4096 MB
Form Factor: DIMM
Set: None
Locator: DIMM1
Bank Locator: BANK1
Type: DDR
Type Detail: Synchronous
Speed: 1333 MHz
Manufacturer: Manufacturer1
Serial Number: SerNum1
Asset Tag: AssetTagNum1
Part Number: PartNum1
Rank: Unknown
Handle 0x0036, DMI type 17, 28 bytes
Memory Device
Array Handle: 0x0030
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 2048 MB
Form Factor: DIMM
Set: None
Locator: DIMM2
Bank Locator: BANK2
Type: DDR
Type Detail: Synchronous
Speed: 1333 MHz
Manufacturer: Manufacturer2
Serial Number: SerNum2
Asset Tag: AssetTagNum2
Part Number: PartNum2
Rank: Unknown
Handle 0x0038, DMI type 17, 28 bytes
Memory Device
Array Handle: 0x0030
Error Information Handle: Not Provided
Total Width: 64 bits
Data Width: 64 bits
Size: 4096 MB
Form Factor: DIMM
Set: None
Locator: DIMM3
Bank Locator: BANK3
Type: DDR
Type Detail: Synchronous
Speed: 1333 MHz
Manufacturer: Manufacturer3
Serial Number: SerNum3
Asset Tag: AssetTagNum3
Part Number: PartNum3
Rank: Unknown
$ free
total used free shared buffers cached
Mem: 6102336 5605508 496828 31384 769868 3664868
-/+ buffers/cache: 1170772 4931564
Swap: 6282236 103584 6178652
貌似free只能看到6G，虽然有12安装。为什么？
更新
顶部的一些输出dmesg：
[ 0.000000] reg 0, base: 0GB, range: 4GB, type WB
[ 0.000000] reg 1, base: 4GB, range: 2GB, type WB
[ 0.000000] reg 2, base: 6GB, range: 512MB, type WB
[ 0.000000] reg 3, base: 3584MB, range: 512MB, type UC
[ 0.000000] total RAM covered: 6144M
更新2
~$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 2.9G 12K 2.9G 1% /dev
tmpfs 596M 21M 576M 4% /run
/dev/sda1 288G 29G 245G 11% /
none 4.0K 0 4.0K 0% /sys/fs/cgroup
none 5.0M 4.0K 5.0M 1% /run/lock
none 3.0G 148K 3.0G 1% /run/shm
none 100M 40K 100M 1% /run/user
更新3
主板是华硕 P7P55-M，内存插槽的物理外观是
手册中的图片如下
我有 2 个 2G 的 DIMM 和 2 个 4G 的 DIMM，并且我按大小将它们插入每种颜色。