Graphics Card VRAM Question

[JigglyPufflez]

So I wanted to get a better understanding of how VRAM on a graphics card is hindered by the bus speed. So if you didn't know the rule is 128bit for every 1GB of VRAM (I think this is the rule correct me if I am wrong<<<) Anyway if for example I had 256bit bus speed but had 4GB vram, does this mean 2GB is only utilised and the other 2GB is LITERALLY unused?/untouched?/as if it is not there?/fake? All help is much appreciated!

[Thunderjolt]

What happens is when you have a bus that is smaller than what is recommend is that it it cannot load enough data from the VRAM to the GPU core to process the data. So when you start using more than what your bus can handle you will start seeing some performance drops it will probably be pretty small though. Like a 256 bit bus can only transfer 32 bytes at one time to the GPU while a 512 bit bus can transfer 64 bytes at one time to the GPU.

Here's a link

http://linustechtips.com/main/topic/44197-memory-bus-size-and-how-it-effects-your-vram-usage/

[xAcid9]

So I wanted to get a better understanding of how VRAM on a graphics card is hindered by the bus speed. So if you didn't know the rule is 128bit for every 1GB of VRAM (I think this is the rule correct me if I am wrong<<<) Anyway if for example I had 256bit bus speed but had 4GB vram, does this mean 2GB is only utilised and the other 2GB is LITERALLY unused?/untouched?/as if it is not there?/fake? All help is much appreciated!

 

Depend on game engine, screen resolution, texture resolution and graphic settings. I've seen GTX770 4GB hit 3GB in modded Skyrim (ran painfully slow) and over 2GB in rFactor 2 (only in Nordschleife actually) both on 1440p.

 

So 2GB is not enough and 4GB is waste of money. Get that 3GB 384bit GPU instead.

 

 

What happens is when you have a bus that is smaller than what is recommend is that it it cannot load enough data from the VRAM to the GPU core to process the data. So when you start using more than what your bus can handle you will start seeing some performance drops it will probably be pretty small though. Like a 256 bit bus can only transfer 32 bytes at one time to the GPU while a 512 bit bus can transfer 64 bytes at one time to the GPU.

Here's a link

http://linustechtips.com/main/topic/44197-memory-bus-size-and-how-it-effects-your-vram-usage/

 

 

The calculation in that thread is so basic, not even close to real world result. 

[Cwazywazy]

Wait, what? My GPU is 128 bit and is 2GB.. Games like BF4 use almost all of it..

[squirrl]

128bit isn't a "speed" it's the size of the path.

A bus is just a path that data needs to travel to get to the target location, it's clock speed is how fast it transfers.  Think of it like a motorway. The bus is the motorway and it has 128 lanes. the cars are the data. that means that 128  cars can be running on the motorway and reach the destination at the same time. if they are running at a max speed of 1ghz then they will get there in say, 1 second, and if they are running at 2ghz then those 128 cars will get there in 0.5 seconds, therefore the next 128 cars can get there in 1 second, meaning that 256 cars managed to get to the destination on a 128 lane motorway at 2GHZ in the same amount of time as 128 cars running at 1ghz on the same motorway.

 

The bus width AND THE MEMORY CLOCK SPEED must be equally as important. You can't say that 4GB of data can't be pushed through a 256 bit bus if you don't take the speed that the memory can go through the pipeline into consideration.

 

Remember, the GTX 770 has 3.5GHz (7GHZ effective) memory which is some of the fastest memory in a GPU available.

[Leonard]

My contribution is only subject to what i have experienced first hand so i may not cover all other aspects.

 

As far as i have seen and experienced, when you want a GPU with VRAM higher that 2GB get the higher - top tier GPU of that series as they have a higher bus width which handles stuttering better. The lower tier GPUs  with VRAM higher than 2GB most of the time access it best with multi-monitor setups.

[JigglyPufflez]

Depend on game engine, screen resolution, texture resolution and graphic settings. I've seen GTX770 4GB hit 3GB in modded Skyrim (ran painfully slow) and over 2GB in rFactor 2 (only in Nordschleife actually) both on 1440p.

 

So 2GB is not enough and 4GB is waste of money. Get that 3GB 384bit GPU instead.

 

 

 

 

The calculation in that thread is so basic, not even close to real world result. 

Oh so the rest of the of the VRAM still exists and can be used, but is just terribly slow when used?

[JigglyPufflez]

128bit isn't a "speed" it's the size of the path.

A bus is just a path that data needs to travel to get to the target location, it's clock speed is how fast it transfers.  Think of it like a motorway. The bus is the motorway and it has 128 lanes. the cars are the data. that means that 128  cars can be running on the motorway and reach the destination at the same time. if they are running at a max speed of 1ghz then they will get there in say, 1 second, and if they are running at 2ghz then those 128 cars will get there in 0.5 seconds, therefore the next 128 cars can get there in 1 second, meaning that 256 cars managed to get to the destination on a 128 lane motorway at 2GHZ in the same amount of time as 128 cars running at 1ghz on the same motorway.

 

The bus width AND THE MEMORY CLOCK SPEED must be equally as important. You can't say that 4GB of data can't be pushed through a 256 bit bus if you don't take the speed that the memory can go through the pipeline into consideration.

 

Remember, the GTX 770 has 3.5GHz (7GHZ effective) memory which is some of the fastest memory in a GPU available.

Thank you Sir! That was an amazing analogy and helped me understand GPU VRAM much more clearly! But again back to the original, question I have a 4GB card and a 256bit bus, with this bus speed being ideal for 2GB, what happens to the other 2GB left, is it ever used?

 

Edit: What is the difference between memory bus type and memory bandwith?

[Slinkey]

Thank you Sir! That was an amazing analogy and helped me understand GPU VRAM much more clearly! But again back to the original, question I have a 4GB card and a 256bit bus, with this bus speed being ideal for 2GB, what happens to the other 2GB left, is it ever used?

 

Edit: What is the difference between memory bus type and memory bandwith?

Yes it will. It will just get access slower, since the bust "width" is not as high. Basically it is queue up in the traffic lanes.

[squirrl]

Thank you Sir! That was an amazing analogy and helped me understand GPU VRAM much more clearly! But again back to the original, question I have a 4GB card and a 256bit bus, with this bus speed being ideal for 2GB, what happens to the other 2GB left, is it ever used?

 

Edit: What is the difference between memory bus type and memory bandwith?

bus width* The bus doesn't have a speed remember, it's the memory that does.

Not sure what you mean by bus type, but bandwith is the product of the speed of the memory and the width of the bus

[JigglyPufflez]

bus width* The bus doesn't have a speed remember, it's the memory that does.

Not sure what you mean by bus type, but bandwith is the product of the speed of the memory and the width of the bus

I was looking at the specs of my GPU (GTX 680) on this website http://videocardz.com/   and it says Memory bus type: 256bit

and memory bandwith: 192.2GB/sec

[squirrl]

I was looking at the specs of my GPU (GTX 680) on this website http://videocardz.com/   and it says Memory bus type: 256bit

and memory bandwith: 192.2GB/sec

well then bus type is just bus width then.