Why is not all RAM available?

Question

laptops

only 6.45 out of 8gb is freely used, why?

inxi -v5

System: Kernel: 5.3.0-24-generic x86_64 bits: 64 compiler: gcc v: 9.2.1 Console: tty 1
Distro: Ubuntu 19.10 (Eoan Ermine)
Machine: Type: Laptop System: LENOVO product: 20160 v: Lenovo V580c serial: WB12770768
Mobo: LENOVO model: 20160 serial: INVALID UEFI [Legacy]: LENOVO v: H1ET75WW(1.18) date: 06/27/2013
Memory: RAM: total: 6.45 GiB used: 3.35 GiB (51.9%)
Array-1: capacity: 16 GiB slots: 2 EC: None max module size: 8 GiB note: est.
Device-1: ChannelA-DIMM0 size: 4 GiB speed: 1600 MT/s type: DDR3
Device-2: ChannelB-DIMM0 size: 4 GiB speed: 1600 MT/s type: DDR3
CPU: Topology: Dual Core model: Intel Core i5-3230M bits: 64 type: MT MCP arch: Ivy Bridge rev: 9 L2 cache: 3072 KiB
flags: avx lm nx pae sse sse2 sse3 sse4_1 sse4_2 ssse3 vmx bogomips: 20753
Speed: 1198 MHz min/max: 1200/3200 MHz Core speeds (MHz): 1: 1220 2: 1216 3: 1230 4: 1243
Graphics: Device-1: Intel 3rd Gen Core processor Graphics vendor: Lenovo driver: i915 v: kernel bus ID: 00:02.0
Device-2: NVIDIA GK208M [GeForce GT 740M] driver: nvidia v: 390.129 bus ID: 01:00.0
Display: server: X.Org 1.20.5 driver: modesetting,nvidia unloaded: fbdev,nouveau,vesa resolution: 1366x768~60Hz
OpenGL: renderer: GeForce GT 740M/PCIe/SSE2 v: 4.6.0 NVIDIA 390.129 direct render: Yes
Audio: Device-1: Intel 7 Series/C216 Family High Definition Audio vendor: Lenovo driver: snd_hda_intel v: kernel
bus ID: 00:1b.0
Sound Server: ALSA v: k5.3.0-24-generic
Network: Device-1: Broadcom and subsidiaries BCM43142 802.11b/g/n vendor: Lenovo driver: wl v: kernel port: 3000
bus ID: 03:00.0
IF: wlp3s0 state: up mac: 48:d2:24:f8:f6:e4
Device-2: Realtek RTL8111/8168/8411 PCI Express Gigabit Ethernet vendor: Lenovo driver: r8169 v: kernel port: 2000
bus ID: 04:00.0
IF: enp4s0 state: down mac: 3c:97:0e:c7:ac:da
Info: Processes: 224 Uptime: 6d 20h 46m Init: systemd runlevel: 5 Compilers: gcc: 9.2.1 Shell: bash v: 5.0.3 inxi: 3.0.36

lshw -C memory

*-cache:0
description: L1 cache
physical id: 7
slot: L1-Cache
size: 32KiB
capacity: 32KiB
capabilities: internal write-through instruction
configuration: level=1
*-cache:1
description: L2 cache
physical id: 8
slot: L2-Cache
size: 256KiB
capacity: 256KiB
capabilities: internal write-through unified
configuration: level=2
*-cache:2
description: L3 cache
physical id: 9
slot: L3-Cache
size: 3MiB
capacity: 3MiB
capabilities: internal write-back unified
configuration: level=3
*-cache
description: L1 cache
physical id: 6
slot: L1-Cache
size: 32KiB
capacity: 32KiB
capabilities: internal write-through data
configuration: level=1
*-memory
description: System Memory
physical id: b
slot: System board or motherboard
size: 8GiB
*-bank:0
description: SODIMM DDR3 Synchronous 1600 MHz (0,6 ns)
product: 99U5469-041.A00LF
vendor: Kingston
physical id: 0
serial: 4B316671
slot: ChannelA-DIMM0
size: 4GiB
width: 64 bits
clock: 1600MHz (0.6ns)
*-bank:1
description: SODIMM DDR3 Synchronous 1600 MHz (0,6 ns)
product: SHARETRONIC
vendor: 0000
physical id: 1
serial: B0752C01
slot: ChannelB-DIMM0
size: 4GiB
width: 64 bits
clock: 1600MHz (0.6ns)
*-firmware
description: BIOS
vendor: LENOVO
physical id: 0
version: H1ET75WW(1.18)
date: 06/27/2013
size: 128KiB
capacity: 12MiB
capabilities: pci pnp upgrade shadowing cdboot bootselect edd int13floppy720 int5printscreen int9keyboard int14serial int17printer int10video acpi usb biosbootspecification uefi

cat /proc/meminfo

MemTotal: 6767812 kB
MemFree: 2353996 kB
MemAvailable: 2934580 kB
Buffers: 93748 kB
Cached: 875824 kB
SwapCached: 9332 kB
Active: 2840928 kB
Inactive: 1039752 kB
Active(anon): 2220572 kB
Inactive(anon): 909556 kB
Active(file): 620356 kB
Inactive(file): 130196 kB
Unevictable: 320 kB
Mlocked: 16 kB
SwapTotal: 6297444 kB
SwapFree: 6213772 kB
Dirty: 212 kB
Writeback: 0 kB
AnonPages: 2905208 kB
Mapped: 642776 kB
Shmem: 219028 kB
KReclaimable: 100520 kB
Slab: 245240 kB
SReclaimable: 100520 kB
SUnreclaim: 144720 kB
KernelStack: 13008 kB
PageTables: 37552 kB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 9681348 kB
Committed_AS: 8526356 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 61500 kB
VmallocChunk: 0 kB
Percpu: 5920 kB
HardwareCorrupted: 0 kB
AnonHugePages: 0 kB
ShmemHugePages: 0 kB
ShmemPmdMapped: 0 kB
CmaTotal: 0 kB
CmaFree: 0 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 0 kB
DirectMap4k: 1171712 kB
DirectMap2M: 5812224 kB