Hexus.net with original information from Reddit user now listed actual detail of the Surface book’s discrete GPU. So what’s the expected performance?
So one on the left is what’s inside Surface book, and one of the left is existing NVIDIA GPU 940M. They are indeed very similar in specification. However, if you are not familiar with details of GPU, you may noticed despite their similarity, Surface Book GPU is slightly lower in its specs essentially most categories. The most noticeable number is Memory Size, which is half of the 940M. However, Memory type GDDR5 compared to DDR3 is superior. So how is half the memory size, use of better memory type result in actual performance?
First let’s take a look at 940M’s perfomance relative to Intel Iris 6100, which is used in Macbook Pro 13 inch.
Intel Iris 6100 (Macbook Pro 13 inch)
3DMark 11: Median 1828
3DMark Vantage: 5717
3DMark 06: 8764
Cinebench R11.5: 27.2
Crysis 3 Medium: 22 fps
3DMark 11 – 2467.5 (1.3x)
3DMark Vantage – 6942.5 (1.2x)
3DMark 06 0 11920 (1.36x)
Cinebench R11.5 – 41.5 (1.52x)
Crysis 3 Medium: 24 fps (1.09x)
So if it is equivalent to 940M performance, there is no way this is 2x better performance than the Macbook Pro 13 inch.
GDDR5 vs. DDR3
So if Microsoft statement is to be believed, the use of GDDR5 despite half the memory size must be the key. I did some internet search about this matter and despite multiple questions about this topic, nobody seemed to have a concise, logically accurate answer to this.
In short, GDDR5 is memory based on the DDR3 but built more specifically for GPU in mind. Analogy here I make up is tablet vs. desktop. You may even pay same money but the form factor is so different due to its usage purpose. So one is emphasizing on portability, quick boot, long battery life whereas other is after performance. Memory use between graphics card and system memory is similarly different; therefore, emphasis is different.
The hardest part to find was so what if we have everything being identical and replace DDR3 to GDDR5, what’s the performance gain?
Here someone posted a comparison on relatively similar chip to compare GPU speed based ont he difference between DDR3 and GDDR5. The key is memory band width difference is 2.22x higher in GDDR-5. The performance gain is at best 19% on 3DMark Vantage score but merely 0.5% on 3DMark 11. Article from MSI had GTX 850M chip tested between GDDR5 and DDR3 version.
GPU Memory Frequency Data per Second Bandwidth Gap GTX850M GDDR5 5000MHz, 128bit 80GB/s 2.5x faster than DDR3 GTX850M DDR3 2000MHz, 128bit 32GB/s 100%
In above, the bandwidth difference is 2.5. So I am not sure GDDR-5 always have a fixed proportionally higher bandwidth vs. design dependent when compared to DDR-3 as 2.22 and 2.5 are similar but not exactly the same. Regardless, GDDR-5 performs better than DDR3 but how much remains to be unanswered.
Back to 755M
At this point, I will try defending myself a little. Recently, based on the simple math of 2x performance against highest model Macbook Pro 13 inch, I concluded GT 755M may potentially be performance equivalent of the dGPU. Below is again, it’s benchmark scores.
3DMark 11: Median 2877.5
3DMark Vantage: 11600
3DMark 06: 15861
Cinebench R11.5: 54.6
Crysis 3 Medium: 49.4 fps
This is far closer to 2x performance than 940M in benchmark scores and better performance than the 940M.
At first glance, it does appear similar to 940M GPU but use of GDDR-5 instead of DDR-3 should provide sufficient upgrade in its performance. The question remains how much and whether it is enough to give 2x performance boost as Microsoft claims remain to be seen until its official release and someone runs benchmark tests. One caution here is if it truly turns out to be 940M equivalent of performance, it merely provides 1.3x performance boost compared to Macbook Pro 13 inch at least on benchmark scores and real life difference may even be less. What this means is that since Macbook Pro will eventually be updating to newer Skylake based GPU where there will be its own performance boost, the difference may even be less. So let’s keep our fingers crossed that the truly this is a custom GPU and performance wise no where near the 940M and Microsoft claim of 2x performance holds true.