MSI GT70 - Who Do I Believe?

I have an MSI GT70, with an Nvidia GTX 870M Graphics card.

GPU-Z claims my 870 has 3GB of 'memory'.

But Can You Run It claims:

Video Card 1 NVIDIA GeForce GTX 870M
Manufacturer NVIDIA
Chipset GeForce GTX 870M
Dedicated Memory 6.2 GB
Total Memory 4.0 GB

So who do I believe? And what is the difference between 'Dedicated Memory (6.2GB)', and 'Total Memory (4.0GB)'?

I know that MSI supposedly added an additional 3GB to some of the GTX 870's in certain models of the GT70.

Thanks for any help!

 

Dedicated video memory is memory on the video card itself. Shared memory is part of your system's RAM that is "given to" the video card for use when it needs to process images. Since dedicated memory is on the card, the chips and the bus to access it are under the card's control, so access is typically much faster and at a higher bandwidth. For shared memory, the card has to use the (shared) system bus and the normal system RAM chips, which increase access time (a lot, typically).
You have 6.2 GB dedicated video memory because you have 32GB Ram memory, but GTX 870M has on board itself 3GB video memory. Also, your CPU has 1GB shared memory so that is also calculated in total memory. MSI had some GTX 870M with 6GB video memory which is better for higher resolutions and GPU heavy games.

 

You can believe GPU z.

 

Which GT70 do you have. The Dominator-895 had a 870M 3GB and the Dominator-893 had a 870M 6GB.

 

Thanks to all for taking the time to clear up my confusion. Much appreciated!!

P.S. I'm pretty sure it's an 895.