8GB Memory for Alienware x51 R3 Desktop DDR4 PC4-17000 2133 MHz Non-ECC DIMM (PARTS-QUICK Brand) at Amazon.com
parts-quick 16GB Memory for Alienware x51 R3 Desktop DDR4 PC4-17000 2133MHz Non-ECC DIMM RAM at Amazon.com
Dell Alienware X51 R3 AX51R3-6510BLK Desktop PC with Intel Core i5-6400 Processor, 8GB Memory, 1TB Hard Drive and Windows 10 Home (Monitor Not Included) - Walmart.com
How to install/upgrade RAM in the Alienware X51 - YouTube
▻ Alienware X51: How to upgrade your PC RAM (Gaming PC Tutorial/ Guide) - YouTube
Alienware X51 R3 2015 Review: specifications, prices, and more | ديلنا