It seems that the GPU requires more memory bandwidth than the CPU. Discrete graphics all have dedicated fast memory on board. The integrated GPU shares the same system memory as the CPU.
Would that cause a CPU performance drop when using the integrated GPU?
Because it seems that the integrated GPU might consume quite a lot of system memory bandwidth.
I found 2 related benchmarks. But they were not doing any GPU intensive works while benchmarking CPU performance. In real world, I might be using several GPU and CPU intensive apps at the same time.
1) Tom's Hardware Review: Efficiency Comparison: Sandy Bridge Vs. Intel And AMD CPUs
They were using 2 x 2 GB DDR3-2200, Kingmax FLKE85F-B8KJAA FEIS, which provides much more bandwidth than common DDR3-1333. Regarding CPU performance, it seems for both Intel Sandy Bridge and AMD Phenom II, it made no difference using integrated graphics or discrete graphics.
Benchmark Results: Integrated Graphics Performance:
Benchmark Results: Discrete Graphics Performance:
2) This one is quite old, posted 4 years ago: Gigabyte MA69VM-S2 Motherboard on AMD 690V (Socket AM2) Chipset.
The same question were also asked 4 years ago at here.
integrated GPUs share system memory with the CPU anyway. The advantage of the APU design is lower power consumption, and lower latency in communication between the GPU and CPU.
According to intel, least on their designs this could be up to a 4x performance boost
