O Ubuntu 16.04 reconhece apenas 24 GB de RAM de 32 GB

Question

Comprei recentemente um novo PC de mesa com 4x8 GB de RAM. No entanto, o sistema operacional (Ubuntu 16.04, 64 bits) reporta apenas 24 GB de RAM em vez de 32. Eu já verifiquei os sticks fisicamente, eles estão instalados corretamente.

Estou ciente de que o sistema operacional pode ocupar parte da memória, mas como 8 GB de memória RAM ausente parece excessiva e 3x8 é igual a 24, imaginei que deveria perguntar às pessoas que têm mais experiência do que eu. Algumas das ferramentas me dão informações conflitantes (como descrito abaixo) - Não tenho certeza do que está acontecendo e não consegui encontrar nada que resolva meu problema, por isso estou postando aqui.

Deixe-me começar com o hardware relevante :

• Placa principal: Asrock 970M Pro3 970 (suporta até 64 GB)
• RAM: G.Skill D332GB 1600-999 GSK RipjawsX K4, 4x8 GB
• GPU: Asus 4 GB D5 GTX 1050 TI PH (li em algum lugar que a GPU ocupa parte da RAM, não tenho certeza se isso é importante aqui ...)

O que eu já tentei:

Aqui é onde fica interessante ...

• O BIOS informa todas as 4 varas de RAM corretamente
• sudo dmidecode --type memory também detecta todos os 4 sticks
• sudo lshw -class memory mostra 32 GB de RAM também

No entanto ...

• "Sobre este computador" reporta 23,5 GiB
• htop também informa 23.5G
• cat /proc/meminfo saídas 24660520 kB
• free -m vê 24082 MB de RAM
• executar o memtest testou apenas 24 GB de RAM (e não encontrou erros)

Alguém pode explicar o que está acontecendo? Esse comportamento é esperado ou há algo errado?

Aqui está a saída completa dos comandos mencionados acima:

sudo dmidecode - tipo de memória

# dmidecode 3.0
Getting SMBIOS data from sysfs.
SMBIOS 2.7 present.

Handle 0x000D, DMI type 16, 23 bytes
Physical Memory Array
    Location: System Board Or Motherboard
    Use: System Memory
    Error Correction Type: None
    Maximum Capacity: 32 GB
    Error Information Handle: Not Provided
    Number Of Devices: 4

Handle 0x000F, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x000D
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 8192 MB
    Form Factor: DIMM
    Set: None
    Locator: A1_DIMM0
    Bank Locator: A1_BANK0
    Type: DDR3
    Type Detail: Synchronous Unbuffered (Unregistered)
    Speed: 1333 MHz
    Manufacturer: Undefined       
    Serial Number: 00000000  
    Asset Tag: A1_AssetTagNum0
    Part Number: F3-1600C9-8GXM    
    Rank: 2
    Configured Clock Speed: 667 MHz

Handle 0x0011, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x000D
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 8192 MB
    Form Factor: DIMM
    Set: None
    Locator: A1_DIMM1
    Bank Locator: A1_BANK1
    Type: DDR3
    Type Detail: Synchronous Unbuffered (Unregistered)
    Speed: 1333 MHz
    Manufacturer: Undefined       
    Serial Number: 00000000  
    Asset Tag: A1_AssetTagNum1
    Part Number: F3-1600C9-8GXM    
    Rank: 2
    Configured Clock Speed: 667 MHz

Handle 0x0013, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x000D
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 8192 MB
    Form Factor: DIMM
    Set: None
    Locator: A1_DIMM2
    Bank Locator: A1_BANK2
    Type: DDR3
    Type Detail: Synchronous Unbuffered (Unregistered)
    Speed: 1333 MHz
    Manufacturer: Undefined       
    Serial Number: 00000000  
    Asset Tag: A1_AssetTagNum2
    Part Number: F3-1600C9-8GXM    
    Rank: 2
    Configured Clock Speed: 667 MHz

Handle 0x0015, DMI type 17, 34 bytes
Memory Device
    Array Handle: 0x000D
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 8192 MB
    Form Factor: DIMM
    Set: None
    Locator: A1_DIMM3
    Bank Locator: A1_BANK3
    Type: DDR3
    Type Detail: Synchronous Unbuffered (Unregistered)
    Speed: 1333 MHz
    Manufacturer: Undefined       
    Serial Number: 00000000  
    Asset Tag: A1_AssetTagNum3
    Part Number: F3-1600C9-8GXM    
    Rank: 2
    Configured Clock Speed: 667 MHz

sudo lshw - memória de classe

  *-firmware              
       description: BIOS
       vendor: American Megatrends Inc.
       physical id: 0
       version: P1.60
       date: 06/17/2016
       size: 64KiB
       capacity: 4032KiB
   capabilities: pci upgrade shadowing cdboot bootselect socketedrom edd int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int9keyboard int14serial     int17printer acpi usb biosbootspecification uefi
  *-cache:0
       description: L1 cache
       physical id: 5
       slot: L1-Cache
       size: 384KiB
       capacity: 384KiB
       clock: 1GHz (1.0ns)
       capabilities: pipeline-burst internal write-back unified
       configuration: level=1
  *-cache:1
       description: L2 cache
       physical id: 6
       slot: L2-Cache
       size: 8MiB
       capacity: 8MiB
       clock: 1GHz (1.0ns)
       capabilities: pipeline-burst internal write-back unified
       configuration: level=2
  *-cache:2
       description: L3 cache
       physical id: 7
       slot: L3-Cache
       size: 8MiB
       capacity: 8MiB
       clock: 1GHz (1.0ns)
       capabilities: pipeline-burst internal write-back unified
       configuration: level=3
  *-memory
       description: System Memory
       physical id: d
       slot: System board or motherboard
       size: 32GiB
     *-bank:0
          description: DIMM DDR3 Synchronous 1333 MHz (0,8 ns)
          product: F3-1600C9-8GXM
          vendor: Undefined
          physical id: 0
          serial: 00000000
          slot: A1_DIMM0
          size: 8GiB
          width: 64 bits
          clock: 1333MHz (0.8ns)
     *-bank:1
          description: DIMM DDR3 Synchronous 1333 MHz (0,8 ns)
          product: F3-1600C9-8GXM
          vendor: Undefined
          physical id: 1
          serial: 00000000
          slot: A1_DIMM1
          size: 8GiB
          width: 64 bits
          clock: 1333MHz (0.8ns)
     *-bank:2
          description: DIMM DDR3 Synchronous 1333 MHz (0,8 ns)
          product: F3-1600C9-8GXM
          vendor: Undefined
          physical id: 2
          serial: 00000000
          slot: A1_DIMM2
          size: 8GiB
          width: 64 bits
          clock: 1333MHz (0.8ns)
     *-bank:3
          description: DIMM DDR3 Synchronous 1333 MHz (0,8 ns)
          product: F3-1600C9-8GXM
          vendor: Undefined
          physical id: 3
          serial: 00000000
          slot: A1_DIMM3
          size: 8GiB
          width: 64 bits
          clock: 1333MHz (0.8ns)

cat / proc / meminfo

MemTotal:       24660520 kB
MemFree:        21122376 kB
MemAvailable:   21926440 kB
Buffers:          140544 kB
Cached:           963872 kB
SwapCached:            0 kB
Active:          2574684 kB
Inactive:         554432 kB
Active(anon):    2027416 kB
Inactive(anon):    71840 kB
Active(file):     547268 kB
Inactive(file):   482592 kB
Unevictable:          48 kB
Mlocked:              48 kB
SwapTotal:      25137148 kB
SwapFree:       25137148 kB
Dirty:                72 kB
Writeback:             0 kB
AnonPages:       2024884 kB
Mapped:           426756 kB
Shmem:             74552 kB
Slab:             170052 kB
SReclaimable:     120684 kB
SUnreclaim:        49368 kB
KernelStack:       11760 kB
PageTables:        48856 kB
NFS_Unstable:          0 kB
Bounce:                0 kB
WritebackTmp:          0 kB
CommitLimit:    37467408 kB
Committed_AS:    8069992 kB
VmallocTotal:   34359738367 kB
VmallocUsed:           0 kB
VmallocChunk:          0 kB
HardwareCorrupted:     0 kB
AnonHugePages:    397312 kB
CmaTotal:              0 kB
CmaFree:               0 kB
HugePages_Total:       0
HugePages_Free:        0
HugePages_Rsvd:        0
HugePages_Surp:        0
Hugepagesize:       2048 kB
DirectMap4k:      277632 kB
DirectMap2M:     7032832 kB
DirectMap1G:    19922944 kB

free -m

              total        used        free      shared  buff/cache        available
Mem:          24082        2263       20553          68        1264       21364
Swap:         24547           0       24547