A separate pool of memory
A graphics card is a small computer in its own right. It has a processor for drawing images, and it has its own memory, kept on the card itself. This is called video memory, graphics memory or VRAM. It is separate from the system memory that the main processor uses.
The reason for the separation is speed. A graphics processor needs to read huge amounts of data many times each second. Memory placed right next to it, designed for very high data transfer rates, can supply that data faster than it could be fetched from elsewhere in the computer.
What lives in video memory
Many different kinds of data share this pool. The main ones are:
- Textures. These are the images wrapped around 3D objects to give them colour and surface detail: the pattern on a brick wall, the grain of a floor, a character’s skin. Textures are usually the largest users of video memory in a modern game.
- Geometry. The shapes that make up characters, buildings and scenery, stored as meshes of points and triangles.
- Frame buffers. The images being drawn, including the finished frame waiting to go to the display, and various intermediate images used during drawing.
- Shaders and effect data. The small programs and supporting data that control lighting, shadows, reflections and other effects.
- Other working data. Items such as lighting information, and data used by techniques like ray tracing or image upscaling.
When a game starts or loads a level, the needed assets are copied from storage into system memory and then into video memory, so the graphics processor can reach them quickly.
Why textures need so much room
A texture is a grid of coloured points, and a detailed one contains a very large number of them. A larger texture holds more detail, but it takes more space in memory. A game may use thousands of them in one scene, along with extra versions at smaller sizes that are used for distant objects. Developers usually compress textures to save room, but the total is still large.
This is why texture quality settings in a game’s menu commonly change the amount of video memory used more than almost any other option. Lower settings use smaller textures or fewer detailed ones; higher settings use larger ones.
What else raises video memory use
Texture settings are not the only factor.
- Screen resolution. Higher resolutions need larger frame buffers and often larger working images for effects. The effect is usually smaller than that of textures, but it adds up. The relationship between detail and screen resolution is covered in more depth elsewhere.
- Visual effects. Features such as ray tracing, high-quality shadows and extra post-processing can require additional buffers and data.
- Larger, more detailed worlds. Scenes with many different objects need more assets loaded at once.
- Mods. Community-made texture packs can raise memory use substantially.
What happens when it runs out
Video memory has a fixed size. If a game needs more than the card has, the system has to make room, typically by keeping some data in system memory and moving it across to the graphics card when it is needed. That path is much slower than reading from video memory directly.
The result depends on the game. Common signs include:
- Sudden stutters or drops in frame rate when turning quickly or entering a new area.
- Textures that appear blurry for a moment, then sharpen, because the game is swapping in detail late.
- In some cases, crashes or error messages.
These symptoms can also have other causes, such as a limited processor or too little system memory, so a symptom alone does not prove that video memory is the problem. Monitoring tools that show video memory use while you play can help you tell the difference.
How much is enough
There is no single right amount. It depends on the games you play, the resolution, and the settings you choose. Older and less demanding games use little; recent games at high resolutions with high texture settings can use a lot. Game developers often publish recommended amounts for specific settings, which is a better guide than general rules.
A few cautions help when comparing cards:
- More video memory does not by itself make a card faster. A card with generous memory but a weaker graphics processor will still be limited by the processor.
- Capacity is only one specification. How fast the memory can move data, called bandwidth, also matters.
- Some games reserve more memory than they strictly need, so a reading showing “high use” may not mean the game is struggling.
When looking at what graphics cards do for performance, treat video memory as one factor among several.
Integrated graphics and shared memory
Some computers do not have a separate graphics card. Their graphics processor is part of the main processor chip and uses a portion of ordinary system memory as its video memory. This is called shared or unified memory. It saves cost and space, but it means the graphics and the rest of the system compete for the same memory, and that memory is typically slower for graphics work than the dedicated kind. Some consoles also use a single shared pool of memory, designed with this arrangement in mind.
Ways to reduce video memory use
If a game is running short of video memory, options usually include:
- Lowering the texture quality setting first, since it often has the largest effect.
- Reducing the resolution.
- Turning down or off the more demanding effects.
- Closing other programs that use the graphics card, such as browsers with many tabs open.
The effect on how the game looks varies, and some players find a reduction in texture quality hardly noticeable while others do.
In short
Video memory is the graphics card’s private workspace, holding the textures, shapes and images it is working with right now. When there is enough, you rarely think about it. When there is not, the card has to fetch data from slower places, and the game stutters or the picture degrades.