NVIDIA GeForce GTX 680M 's Advantages
Boost Clock758MHz
More VRAM (4GB vs 1024GB)
Larger VRAM bandwidth (115.2GB/s vs 14.40GB/s)
1248 additional rendering cores
NVIDIA GeForce GT 820M 's Advantages
Released 1 years and 5 months late
Lower TDP (15W vs 100W)