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To make a long story short, Ubuntu 12.04 64-bit is only detecting 4 GB of RAM even though 8 GB are installed. Here's what I've done so far to rectify the problem:

  • Replaced both RAM sticks, issue persisted.
  • Replaced motherboard, issue persisted.
  • Booted from Live CD to see if it was a software issue, persisted.
  • BIOS detects 8 GB of memory properly but shows it as being in "single channel mode".

When I first put together this system (only a mere 3 weeks ago), it was detecting the proper amount of RAM just fine. Shortly thereafter, I installed a new power supply in the machine (as the original one I had ordered ended up being too small for my the enclosure I have). It seems to me that the problem started after I installed the new power supply.

I've replaced every component in the system since then troubleshooting, but not the power supply. Could this in some way be the problem? If there's some sort of power flow problem, would it cause memory to run in Single Channel Mode? Everything else appears to be working fine... hard drive, blu-ray drive, only thing is that within System Information, I see that the reported CPU speed sometimes jumps between 2700 MHz and 800 MHz. Is that normal for a quad-core system under Ubuntu 12.04?

Thank you.

    output of uname -m:
    x86_64

    output of free -m:


                 total       used       free     shared    buffers     cached
    Mem:          3680       3072        608          0        150       1755
    -/+ buffers/cache:       1166       2513
    Swap:         7912          0       7912



    `*-firmware              
       description: BIOS
       vendor: American Megatrends Inc.
       physical id: 0
       version: P1.50
       date: 02/09/2012
       size: 64KiB
       capacity: 4032KiB
       capabilities: pci upgrade shadowing cdboot bootselect socketedrom edd int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int9keyboard int14serial int17printer acpi usb biosbootspecification
    *-memory
       description: System Memory
       physical id: 6
       slot: System board or motherboard
       size: 8GiB
     *-bank:0
          description: DIMM DDR3 Synchronous 1333 MHz (0.8 ns)
          product: 1333EL Series
          vendor: Undefined
          physical id: 0
          serial: 00000000
          slot: A1_DIMM0
          size: 4GiB
          width: 64 bits
          clock: 1333MHz (0.8ns)
     *-bank:1
          description: DIMM DDR3 Synchronous 1333 MHz (0.8 ns)
          product: Array1_PartNumber1
          vendor: A1_Manufacturer1
          physical id: 1
          serial: A1_SerNum1
          slot: A1_DIMM1
          size: 4GiB
          width: 64 bits
          clock: 1333MHz (0.8ns)
  *-cache:0
       description: L1 cache
       physical id: d
       slot: L1 CACHE
       size: 512KiB
       capacity: 512KiB
       clock: 1GHz (1.0ns)
       capabilities: pipeline-burst internal write-back unified
  *-cache:1
       description: L2 cache
       physical id: e
       slot: L2 CACHE
       size: 4MiB
       capacity: 4MiB
       clock: 1GHz (1.0ns)
       capabilities: pipeline-burst internal write-back unified

Here's the BIOS e820 information:

May 25 04:48:08 Arcturus kernel: [    0.000000] BIOS-provided physical RAM map:
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 0000000000000000 - 000000000009ec00 (usable)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 000000000009ec00 - 00000000000a0000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 0000000000100000 - 00000000bf77c000 (usable)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000bf77c000 - 00000000bf7c5000 (ACPI NVS)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000bf7c5000 - 00000000bf7cd000 (ACPI data)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000bf7cd000 - 00000000bf7d1000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000bf7d1000 - 00000000bf7d6000 (ACPI NVS)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000bf7d6000 - 00000000bfa43000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000bfa43000 - 00000000bfa4a000 (ACPI NVS)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000bfa4a000 - 00000000bfa72000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000bfa72000 - 00000000bfc75000 (ACPI NVS)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000bfc75000 - 00000000bff00000 (usable)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000fec10000 - 00000000fec11000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000fed00000 - 00000000fed01000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000fed61000 - 00000000fed71000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000fed80000 - 00000000fed90000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 00000000ff000000 - 0000000100000000 (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000]  BIOS-e820: 0000000100001000 - 000000012f000000 (usable)
May 25 04:48:08 Arcturus kernel: [    0.000000] NX (Execute Disable) protection: active
May 25 04:48:08 Arcturus kernel: [    0.000000] DMI 2.7 present.
May 25 04:48:08 Arcturus kernel: [    0.000000] DMI: To Be Filled By O.E.M. To Be Filled By O.E.M./A75M-ITX, BIOS P1.50 02/09/2012
May 25 04:48:08 Arcturus kernel: [    0.000000] e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000] e820 remove range: 00000000000a0000 - 0000000000100000 (usable)
May 25 04:48:08 Arcturus kernel: [    0.000000] No AGP bridge found
May 25 04:48:08 Arcturus kernel: [    0.000000] last_pfn = 0x12f000 max_arch_pfn = 0x400000000
May 25 04:48:08 Arcturus kernel: [    0.000000] MTRR default type: uncachable
May 25 04:48:08 Arcturus kernel: [    0.000000] MTRR fixed ranges enabled:
May 25 04:48:08 Arcturus kernel: [    0.000000]   00000-9FFFF write-back
May 25 04:48:08 Arcturus kernel: [    0.000000]   A0000-BFFFF write-through
May 25 04:48:08 Arcturus kernel: [    0.000000]   C0000-CEFFF write-protect
May 25 04:48:08 Arcturus kernel: [    0.000000]   CF000-E7FFF uncachable
May 25 04:48:08 Arcturus kernel: [    0.000000]   E8000-FFFFF write-protect
May 25 04:48:08 Arcturus kernel: [    0.000000] MTRR variable ranges enabled:
May 25 04:48:08 Arcturus kernel: [    0.000000]   0 base 0000000000 mask FF00000000 write-back
May 25 04:48:08 Arcturus kernel: [    0.000000]   1 base 00BFF00000 mask FFFFF00000 uncachable
May 25 04:48:08 Arcturus kernel: [    0.000000]   2 base 00C0000000 mask FFC0000000 uncachable
May 25 04:48:08 Arcturus kernel: [    0.000000]   3 disabled
May 25 04:48:08 Arcturus kernel: [    0.000000]   4 disabled
May 25 04:48:08 Arcturus kernel: [    0.000000]   5 disabled
May 25 04:48:08 Arcturus kernel: [    0.000000]   6 disabled
May 25 04:48:08 Arcturus kernel: [    0.000000]   7 disabled
May 25 04:48:08 Arcturus kernel: [    0.000000] TOM2: 000000013f000000 aka 5104M
May 25 04:48:08 Arcturus kernel: [    0.000000] x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106
May 25 04:48:08 Arcturus kernel: [    0.000000] original variable MTRRs
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 0, base: 0GB, range: 4GB, type WB
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 1, base: 3071MB, range: 1MB, type UC
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 2, base: 3GB, range: 1GB, type UC
May 25 04:48:08 Arcturus kernel: [    0.000000] total RAM covered: 3071M
May 25 04:48:08 Arcturus kernel: [    0.000000] Found optimal setting for mtrr clean up
May 25 04:48:08 Arcturus kernel: [    0.000000]  gran_size: 64K         chunk_size: 2M  num_reg: 3      lose cover RAM: 0G
May 25 04:48:08 Arcturus kernel: [    0.000000] New variable MTRRs
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 0, base: 0GB, range: 2GB, type WB
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 1, base: 2GB, range: 1GB, type WB
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 2, base: 3071MB, range: 1MB, type UC
May 25 04:48:08 Arcturus kernel: [    0.000000] e820 update range: 00000000bff00000 - 0000000100000000 (usable) ==> (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000] last_pfn = 0xbff00 max_arch_pfn = 0x400000000
May 25 04:48:08 Arcturus kernel: [    0.000000] found SMP MP-table at [ffff8800000fcf10] fcf10
May 25 04:48:08 Arcturus kernel: [    0.000000] initial memory mapped : 0 - 20000000
May 25 04:48:08 Arcturus kernel: [    0.000000]   7 disabled
May 25 04:48:08 Arcturus kernel: [    0.000000] TOM2: 000000013f000000 aka 5104M
May 25 04:48:08 Arcturus kernel: [    0.000000] x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106
May 25 04:48:08 Arcturus kernel: [    0.000000] original variable MTRRs
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 0, base: 0GB, range: 4GB, type WB
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 1, base: 3071MB, range: 1MB, type UC
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 2, base: 3GB, range: 1GB, type UC
May 25 04:48:08 Arcturus kernel: [    0.000000] total RAM covered: 3071M
May 25 04:48:08 Arcturus kernel: [    0.000000] Found optimal setting for mtrr clean up
May 25 04:48:08 Arcturus kernel: [    0.000000]  gran_size: 64K         chunk_size: 2M  num_reg: 3      lose cover RAM: 0G
May 25 04:48:08 Arcturus kernel: [    0.000000] New variable MTRRs
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 0, base: 0GB, range: 2GB, type WB
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 1, base: 2GB, range: 1GB, type WB
May 25 04:48:08 Arcturus kernel: [    0.000000] reg 2, base: 3071MB, range: 1MB, type UC
May 25 04:48:08 Arcturus kernel: [    0.000000] e820 update range: 00000000bff00000 - 0000000100000000 (usable) ==> (reserved)
May 25 04:48:08 Arcturus kernel: [    0.000000] last_pfn = 0xbff00 max_arch_pfn = 0x400000000
May 25 04:48:08 Arcturus kernel: [    0.000000] found SMP MP-table at [ffff8800000fcf10] fcf10
May 25 04:48:08 Arcturus kernel: [    0.000000] initial memory mapped : 0 - 20000000
share|improve this question
    
post output uname -m and free -m –  izx May 25 '12 at 1:26
    
updated my post with information requested... thank you. –  specik May 25 '12 at 1:35
    
You can try sudo lshw -C memory to get more details. –  user unknown May 25 '12 at 1:59
    
posted the result of that command. sees both memory DIMMs. i'm puzzled. can the power supply maybe be the culprit? –  specik May 25 '12 at 2:08
    
Check dmesg or /var/log/kern.log for the section that lists the bios e820 map and add that to your question. –  psusi May 25 '12 at 2:16
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2 Answers

There was another post on askubuntu where someone mentioned a similar case, they were only able to see 3 Gbs out of 16. Here is the link Perhaps you can check through the dmesg output to see if the kernel is reporting any similar bug problems during boot up.

share|improve this answer
    
I saw that case you mentioned earlier. I see no such BIOS bug output in my dmesg. –  specik May 25 '12 at 1:51
    
What Motherboard did you use when building your setup? –  itnet7 May 25 '12 at 2:09
    
ASRock A75M-ITX –  specik May 25 '12 at 2:12
    
... and the output of uname -a –  itnet7 May 25 '12 at 2:16
    
Linux Arcturus 3.2.0-24-generic #37-Ubuntu SMP Wed Apr 25 08:43:22 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux –  specik May 25 '12 at 2:34
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Your bios is not reporting the ram to the kernel in the e820 map, so you appear to have a bios bug. Check with your motherboard maker to see if they have a bios update to fix it.

share|improve this answer
    
Thank you for the information. I will check that. What I find odd though is that when I first built the system, it did report the 8GB of RAM. I stopped doing so right around the time that I replaced the power supply in the system... but I don't see how a power supply could cause a weird issue like this. –  specik May 25 '12 at 2:55
    
Additionally, the BIOS sees both RAM sticks... but reports them as being in "Single Channel Mode". –  specik May 25 '12 at 3:01
    
So updated my BIOS software to the latest version... issue persists. At this point, I'm just frustrated. I bought this box to serve as a XBMC media center and it's been a pretty big nightmare. –  specik May 25 '12 at 12:47
    
@specik, looks like you're going to need to find a new motherboard vendor. –  psusi May 25 '12 at 18:59
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