4GB Installed only 2GB usable

Computer Type: PC/Desktop
System Manufacturer/Model Number: Custom assembled by me :}
OS: Win-7-Pro64bit 7-H-Prem-64bit
CPU: i7-5930K 2nd i9-9940x both water blocked VRM's too
Motherboard: ASUS SABERTOOTH X99 2nd ASUS x299 Apex
Memory: Trident-z 3200C14 2nd Trident-z 3600C16
Graphics Card: EVGA 1080ti ftw3 2nd Titan Xp both water blocked
Sound Card: Built-in Realtek
Monitor(s) Displays: 1-AOC G2460PG 24"G-Sync 144Hz/ 2nd 1-ASUS VG248QE 24" 144Hz
Screen Resolution: 1920 x 1080 144Hz
Keyboard: Logitech G710+/ 2nd Logitech G910
Mouse: 2-RedDragon M901 Perdition 16400 dpi Gaming mouse = wired
PSU: EVGA SuperNOVA 1000-P2 2nd 1200-P2
Case: 2-Corsair Obsidian Series 450D Black ATX Mid Tower
Cooling: Custom water loops
Hard Drives: 2-Samsung M.2 Evo & Evo Plus 2-Samsung 850 EVO 500GB SSD's/ 3-2.5 W.D. Black 1tb-&3-1tb/3-3.5 WD Black 1tb hdd's
Internet Speed: Comcast Ping 19ms 89.31mbps download speed 6.12mbps upload
Browser: FireFox & Pale moon
Antivirus: Malwarebytes Pro/ Superantispyware Pro
Other Info: 2nd ASUS X299 Apex/Intel i9-9940x with Custom water loop/7H-Prem-x64/Corsair 450D case/Ram Trident-z 3600C16 4x8gb / Samsung970Evo plus 500gb SSD/Dual ssd EZ swap evo/PSU EVGA SuperNova 1200w-P2 80+Platinum/GPU Titan Xp /8-ML-140 on push-pull on 2-280GTX rads