Por que a memória instalada não é igual a “total memory”

Question

Estou executando o Linux (Mint 17) no novo laptop (Asus X550ZA) que tem 8GB de RAM. O BIOS mostra 8GB, mas quando eu mostro / proc / meminfo, ele mostra apenas 3,4GB:

 $ sudo cat /proc/meminfo
MemTotal:        3411176 kB
MemFree:          122224 kB
MemAvailable:    1924580 kB

Quando mostro a memória física instalada, mostra os 8GB. Então, o que aconteceu com meus outros 4,5 GB de memória? O que está alocando isso? Ah, estou executando um sistema operacional de 64 bits (Linux gregh-X550ZA 3.19.0-33-genérico # 38 ~ 14.04.1-Ubuntu SMP sex 6 de novembro de 18:17:28 UTC 2015 x86_64 x86_64 x86_64 GNU / Linux)

$ sudo dmidecode --type memory

Handle 0x0031, DMI type 16, 23 bytes
Physical Memory Array
    Location: System Board Or Motherboard
    Use: System Memory
    Error Correction Type: None
    Maximum Capacity: 8 GB
    Error Information Handle: Not Provided
    Number Of Devices: 2

Handle 0x0033, DMI type 17, 40 bytes
Memory Device
    Array Handle: 0x0031
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: SODIMM
    Set: None
    Locator: DIMM 0
    Bank Locator: CHANNEL A
    Type: DDR3
    Type Detail: Synchronous Unbuffered (Unregistered)
    Speed: 1600 MHz
    Manufacturer: Hynix/Hyundai
    Serial Number: 1219ADB5
    Asset Tag: A1_AssetTagNum0
    Part Number: HMT451S6BFR8A-PB  
    Rank: 1
    Configured Clock Speed: 1600 MHz
    Minimum voltage:  1.350 V
    Maximum voltage:  1.500 V
    Configured voltage:  1.500 V

Handle 0x0034, DMI type 17, 40 bytes
Memory Device
    Array Handle: 0x0031
    Error Information Handle: Not Provided
    Total Width: 64 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: SODIMM
    Set: None
    Locator: DIMM 0
    Bank Locator: CHANNEL B
    Type: DDR3
    Type Detail: Synchronous Unbuffered (Unregistered)
    Speed: 1600 MHz
    Manufacturer: Hynix/Hyundai
    Serial Number: 1259ADB8
    Asset Tag: A1_AssetTagNum1
    Part Number: HMT451S6BFR8A-PB  
    Rank: 1
    Configured Clock Speed: 1600 MHz
    Minimum voltage:  1.350 V
    Maximum voltage:  1.500 V
    Configured voltage:  1.500 V