Explain VRAM

[nO_d3N1AL]

Out of curiosity, I just want some concepts to be clarified by some computer scientist. Here are my questions:

What is the difference between dedicated video memory and system memory?

If I have a 1GB graphics card, what happens to the SHARED memory (e.g. 3GB)?

What is VRAM used for? What features in games require it?

How come you can run games like L4D2 with an internal GPU (such as Intel HD 4000) on high settings even though it only has 32MB dedicated video memory?

Thanks for the replies in advance.

[_I_]

system ram is used for the os and programs that run

video ram is used for the video card, desktop will use around 10-30mb of v-ram
some games can use upto around 2-4g

shared ram is when a gpu uses system ram for the gpu
its way slower than dedicated ram for the video card

the intel hd cards use shared ram, the gpu is on the cpu so it has faster access to it
shared ram will allocate whats needed as its needs it
source games will use around 128m-512m of vram

[nO_d3N1AL]

But what is the DIFFERENCE? How is (dedicated) video memory different to system memory? A 5 year-old can deduce that Vram is for graphics card but doesn't explain what it actually is

[_I_]

vram is only or displaying pictures on the monitor
frame buffer and models/textures in 3d games

[nO_d3N1AL]

_I_ eredeti hozzászólása:

vram is only or displaying pictures on the monitor
frame buffer and models/textures in 3d games

Ah ok. So in effect it's just used so that the information that is sent directly to the display device can be dealt with on the card itself rather than going through the main system processor, then through CPU then back to GPU etc. or something like that?

[senseidongen]

It can be the same type of RAM (DDR3) for cheaper cards, or it can be faster, more expensive GDDR5 type. GDDR5 is based on DDR3 but it has a much higher clockspeed (and therefore bandwidth) and looser latency timings. In the case of a discrete GPU, VRAM is simply RAM sticks physically attached to the graphics card as opposed to system RAM which slots into the motherboard.

Put simply, it is memory dedicated to the graphics card and stores stuff like textures and models currently in use, as well as data waiting to be processed and output as frames on screen. However, it isn't just the GPU that needs data storage whilst rendering a game: the CPU is also busy doing stuff like physics calculations and AI, plus the CPU and GPU need to talk to each other so hence you have shared RAM that is used for both the CPU and GPU. Also, if you run out of VRAM, the GPU will rely on the system RAM to make up the difference (though this is slower and hence why you need a certain amount of VRAM).

When talking about integrated graphics (such as intel HD4000 or an AMD APU), the distinction is slightly different as it simply becomes a portion of the main system RAM that may not be used for anything else besides graphics processing. In the case of the 32 MB, this is basically the minimum to maintain what's on screen whilst on the desktop (otherwise the display could disappear I guess). Obviously when running a game, the integrated graphics will simply use more system RAM beyond the bare minimum allocated to it.

[nO_d3N1AL]

Great explanation, thanks. So the dedicated graphics memory is used to process only the graphics stuff such as frames, textures and lighting whilst the shared memory can be used for more general processing? What I don't get is when a graphics card has 4GB total memory but 1GB dedicated, the other 3GB isn't magically added on to my main system memory (say I had 8GB, then with the graphics card shouldn't I have 11GB system RAM?)

[senseidongen]

nO_d3N1AL eredeti hozzászólása:

Great explanation, thanks. So the dedicated graphics memory is used to process only the graphics stuff such as frames, textures and lighting whilst the shared memory can be used for more general processing? What I don't get is when a graphics card has 4GB total memory but 1GB dedicated, the other 3GB isn't magically added on to my main system memory (say I had 8GB, then with the graphics card shouldn't I have 11GB system RAM?)

In that case, the card would have 1GB worth of RAM sticks attached to it and the remaining 3GB would come out of the 8GB system RAM. So if it used all that memory, you'd have 1GB of on card memory in use, 3GB of system RAM in use and 5GB left for whatever else is going on (typically at least 1.5GB for Windows at all times, for example)

[nO_d3N1AL]

senseidongen eredeti hozzászólása:

nO_d3N1AL eredeti hozzászólása:

Great explanation, thanks. So the dedicated graphics memory is used to process only the graphics stuff such as frames, textures and lighting whilst the shared memory can be used for more general processing? What I don't get is when a graphics card has 4GB total memory but 1GB dedicated, the other 3GB isn't magically added on to my main system memory (say I had 8GB, then with the graphics card shouldn't I have 11GB system RAM?)

In that case, the card would have 1GB worth of RAM sticks attached to it and the remaining 3GB would come out of the 8GB system RAM. So if it used all that memory, you'd have 1GB of on card memory in use, 3GB of system RAM in use and 5GB left for whatever else is going on (typically at least 1.5GB for Windows at all times, for example)

Ah right. So when my graphics card says it has 3GB shared, it means that it is "entitled" to use up to 3GB of my main system RAM; not adding 3GB itself

[senseidongen]

Exactly :)

[nO_d3N1AL]

Cool, cheers!