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I have Ubuntu 12.04 32 bit with PAE enable.

Linux alptugay-MS-7693 3.2.0-39-generic-pae #62-Ubuntu SMP Wed Feb 27 22:25:11 UTC 2013 i686 athlon i386 GNU/Linux

I have been using my computer with 4 GB of ram. The output of free -m shows

             total       used       free     shared    buffers     cached
Mem:          3995       1536       2458          0         75        484

I have now added another 4 GB ram. Which is identical to the other ram. But Ubuntu doesn't see it. The output of free did not change. But my bios sees 8GB ram. Also the output of lshw shows my 8 GB rams:

 *-memory
      description: System Memory
      physical id: 27
      slot: System board or motherboard
      size: 8GiB
    *-bank:0
         description: DIMM DDR3 Synchronous 667 MHz (1.5 ns)
         product: Array1_PartNumber0
         vendor: A1_Manufacturer0
         physical id: 0
         serial: A1_SerNum0
         slot: A1_DIMM0
         size: 4GiB
         width: 64 bits
         clock: 667MHz (1.5ns)
    *-bank:1
         description: DIMM Synchronous [empty]
         product: Array1_PartNumber1
         vendor: A1_Manufacturer1
         physical id: 1
         serial: A1_SerNum1
         slot: A1_DIMM1
    *-bank:2
         description: DIMM DDR3 Synchronous 667 MHz (1.5 ns)
         product: Array1_PartNumber2
         vendor: A1_Manufacturer2
         physical id: 2
         serial: A1_SerNum2
         slot: A1_DIMM2
         size: 4GiB
         width: 64 bits
         clock: 667MHz (1.5ns)
    *-bank:3
         description: DIMM Synchronous [empty]
         product: Array1_PartNumber3
         vendor: A1_Manufacturer3
         physical id: 3
         serial: A1_SerNum3
         slot: A1_DIMM3

And this is the output of dmidecode

Handle 0x0027, DMI type 16, 23 bytes
Physical Memory Array
    Location: System Board Or Motherboard
    Use: System Memory
    Error Correction Type: Multi-bit ECC
    Maximum Capacity: 32 GB
    Error Information Handle: Not Provided
    Number Of Devices: 4

Handle 0x0028, DMI type 19, 31 bytes
Memory Array Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x0013F0003FF
    Range Size: 5104 MB
    Physical Array Handle: 0x0027
    Partition Width: 255

Handle 0x0029, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x0027
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: DIMM
    Set: None
    Locator: A1_DIMM0
    Bank Locator: A1_BANK0
    Type: DDR3
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: A1_Manufacturer0
    Serial Number: A1_SerNum0
    Asset Tag: A1_AssetTagNum0
    Part Number: Array1_PartNumber0
    Rank: Unknown
    Configured Clock Speed: 933 MHz

Handle 0x002A, DMI type 20, 35 bytes
Memory Device Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x000FFFFFFFF
    Range Size: 4 GB
    Physical Device Handle: 0x0029
    Memory Array Mapped Address Handle: 0x0028
    Partition Row Position: <OUT OF SPEC>
    Interleave Position: Unknown
    Interleaved Data Depth: Unknown

Handle 0x002B, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x0027
    Error Information Handle: Not Provided
    Total Width: Unknown
    Data Width: 64 bits
    Size: No Module Installed
    Form Factor: DIMM
    Set: None
    Locator: A1_DIMM1
    Bank Locator: A1_BANK1
    Type: Unknown
    Type Detail: Synchronous
    Speed: Unknown
    Manufacturer: A1_Manufacturer1
    Serial Number: A1_SerNum1
    Asset Tag: A1_AssetTagNum1
    Part Number: Array1_PartNumber1
    Rank: Unknown
    Configured Clock Speed: Unknown

Handle 0x002C, DMI type 126, 35 bytes
Inactive

Handle 0x002D, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x0027
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: DIMM
    Set: None
    Locator: A1_DIMM2
    Bank Locator: A1_BANK2
    Type: DDR3
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: A1_Manufacturer2
    Serial Number: A1_SerNum2
    Asset Tag: A1_AssetTagNum2
    Part Number: Array1_PartNumber2
    Rank: Unknown
    Configured Clock Speed: 933 MHz

Handle 0x002E, DMI type 20, 35 bytes
Memory Device Mapped Address
    Starting Address: 0x00000000000
    Ending Address: 0x000000003FF
    Range Size: 1 kB
    Physical Device Handle: 0x002D
    Memory Array Mapped Address Handle: 0x0028
    Partition Row Position: <OUT OF SPEC>
    Interleave Position: Unknown
    Interleaved Data Depth: Unknown

Handle 0x002F, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x0027
    Error Information Handle: Not Provided
    Total Width: Unknown
    Data Width: 64 bits
    Size: No Module Installed
    Form Factor: DIMM
    Set: None
    Locator: A1_DIMM3
    Bank Locator: A1_BANK3
    Type: Unknown
    Type Detail: Synchronous
    Speed: Unknown
    Manufacturer: A1_Manufacturer3
    Serial Number: A1_SerNum3
    Asset Tag: A1_AssetTagNum3
    Part Number: Array1_PartNumber3
    Rank: Unknown
    Configured Clock Speed: Unknown

Handle 0x0030, DMI type 126, 35 bytes
Inactive

What may be the problem?

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Check the BIOS for a memory hole/mapping setting; this may be causing this, although a cutoff at 3.1 GB is more usual. –  oKtosiTe Mar 27 '13 at 8:37
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1 Answer

up vote 3 down vote accepted

Changing the ram slots worked.

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