AMD Ryzen 7 7840H's Advantages
Released 2 years and 10 months late
Larger memory bandwidth (89.6GB/s vs 68.27GB/s)
Newer PCIe version (4 vs 3.0)
Higher base frequency (3.8GHz vs 3.0GHz)
Larger L3 cache size (16MB vs 8MB)
More modern manufacturing process (4nm vs 7nm)
AMD Ryzen 9 4900HS's Advantages
Higher specification of memory (LPDDR4X-4266 vs DDR5-5600)