NVIDIA GeForce 840M 's Advantages
Released 5 years and 3 months late
Boost Clock1124MHz
More VRAM (2GB vs 256GB)
352 additional rendering cores
NVIDIA GeForce GT 120M Mac Edition 's Advantages
Larger VRAM bandwidth (25.34GB/s vs 16.02GB/s)
Lower TDP (14W vs 33W)