I have Ubuntu 18.04 dual booted with Windows 10. Windows 10 shows full 8 GB RAM.

But in Ubuntu it shows only 6.8 GB.

Is there any way to make it near 8 GB or is this natural?

~$ free

              total        used        free      shared  buff/cache   available

Mem:        7097484     1775180     3633172       67964     1689132     4994508

Swap:       1000444           0     1000444

After turning the swap area off,

~$ free

              total        used        free      shared  buff/cache   available

Mem:        7097484     1776700     4761256      111464      559528     4949096

Swap:             0           0           0

Output

~# dmesg | grep -i memory:

[    0.000000] PM: Registered nosave memory: [mem 0x00000000-0x00000fff]

[    0.000000] PM: Registered nosave memory: [mem 0x00087000-0x00087fff]

[    0.000000] PM: Registered nosave memory: [mem 0x000a0000-0x000bffff]

[    0.000000] PM: Registered nosave memory: [mem 0x000c0000-0x000fffff]

[    0.000000] PM: Registered nosave memory: [mem 0x09b00000-0x09dfffff]

[    0.000000] PM: Registered nosave memory: [mem 0x09f00000-0x09f09fff]

[    0.000000] PM: Registered nosave memory: [mem 0x6427a000-0x64b79fff]

[    0.000000] PM: Registered nosave memory: [mem 0x6b58f000-0x6b78efff]

[    0.000000] PM: Registered nosave memory: [mem 0x6b78f000-0x6d78efff]

[    0.000000] PM: Registered nosave memory: [mem 0x6d78f000-0x6f78efff]

[    0.000000] PM: Registered nosave memory: [mem 0x6f78f000-0x6f7fefff]

[    0.000000] PM: Registered nosave memory: [mem 0x6f800000-0xafffffff]

[    0.000000] PM: Registered nosave memory: [mem 0xb0000000-0xf7ffffff]

[    0.000000] PM: Registered nosave memory: [mem 0xf8000000-0xfbffffff]

[    0.000000] PM: Registered nosave memory: [mem 0xfc000000-0xfebfffff]

[    0.000000] PM: Registered nosave memory: [mem 0xfec00000-0xfec00fff]

[    0.000000] PM: Registered nosave memory: [mem 0xfec01000-0xfec0ffff]

[    0.000000] PM: Registered nosave memory: [mem 0xfec10000-0xfec10fff]

[    0.000000] PM: Registered nosave memory: [mem 0xfec11000-0xfed7ffff]

[    0.000000] PM: Registered nosave memory: [mem 0xfed80000-0xfed80fff]

[    0.000000] PM: Registered nosave memory: [mem 0xfed81000-0xfedfffff]

[    0.000000] PM: Registered nosave memory: [mem 0xfee00000-0xfee00fff]

[    0.000000] PM: Registered nosave memory: [mem 0xfee01000-0xff7fffff]

[    0.000000] PM: Registered nosave memory: [mem 0xff800000-0xfff4ffff]

[    0.000000] PM: Registered nosave memory: [mem 0xfff50000-0xffffffff]

[    0.000000] Memory: 6929972K/7238032K available (12300K kernel code, 2472K rwdata, 4248K rodata, 2408K init, 2416K bss, 308060K reserved, 0K cma-reserved)

[    0.039763] Freeing SMP alternatives memory: 36K

[    1.147121] Freeing initrd memory: 54212K

[  141.519341] Freeing unused kernel memory: 2408K

[  153.310684] Freeing unused kernel memory: 2008K

[  153.317976] Freeing unused kernel memory: 1896K

[  153.869546] [TTM] Zone  kernel: Available graphics memory: 3548742 kiB

[  153.869547] [TTM] Zone   dma32: Available graphics memory: 2097152 kiB