What is a shading unit and a texture mapping unit in a GPU ? and how does it affect blender? in a graphic card spec like here for example


  The GeForce GTX 970 was a performance graphics card by NVIDIA,
  launched in September 2014. Built on the 28 nm process, and based on
  the GM204 graphics processor, in its GM204-200-A1 variant, the card
  supports DirectX 12.0. The GM204 graphics processor is a large chip
  with a die area of 398 mm² and 5,200 million transistors. Unlike the
  fully unlocked GeForce GTX 980, which uses the same GPU but has all
  2048 shaders enabled, NVIDIA has disabled some shading units on the
  GeForce GTX 970 to reach the product's target shader count. It
  features 1664 shading units, 104 texture mapping units and 56 ROPs.
  NVIDIA has placed 4,096 MB GDDR5 memory on the card, which are
  connected using a 256-bit memory interface. The GPU is operating at a
  frequency of 1050 MHz, which can be boosted up to 1178 MHz, memory is
  running at 1753 MHz.  Being a dual-slot card, the NVIDIA GeForce GTX
  970 draws power from 2x 6-pin power connectors, with power draw rated
  at 148 W maximum. Display outputs include: 1x DVI, 1x HDMI, 3x
  DisplayPort. GeForce GTX 970 is connected to the rest of the system
  using a PCI-Express 3.0 x16 interface. The card measures 267 mm in
  length, and features a dual-slot cooling solution. Its price at launch
  was 329 US Dollars.


we have some vocabulary:  

-shading unit

-shaders

-texture mapping units

does thoses caracteristics have any impact inside of blender ?

like the limit of material slot we can have? 

the limit the number of image texture slot we can have? 

the limit the nodes we can have? 

for exemple, a scene with 500 material; 3000 image textures, and a material with a node tree of thousands of nodes, is possible with a gpu, or there's some limit?
These statistics do not impact blender directly. You can have thousands of nodes and shaders and terrabytes of textures if you want and if your PC can handle it. 

This is where these components come back into play. The better a GPU is the better it can handle those things. Your GPU can't hold terrabytes of textures, and you're probably going to kill your rendertimes with a nodes setup thousands of nodes deep. 

The units mentioned here are directly related to the architecture of the card. A texture mapping unit for example is what's actually doing the caculations for UV unwrapping. Having less of them doesn't change the size of your possible UV map, it just means it takes longer to calculate the unwrapping.