Most Dell Alienware gaming laptops feature the letter ‘M’ followed by a number in their name as well as the letter ‘R’ also followed by a number The number after the ‘M’ is the size while the number after the ‘R’ is the model or revision. Alienware m15 R6 features a 15-inch screen and is the sixth revision, which is newer than the Alienware m15 R4 of the same size.