A graphics card is essentially composed of a GPU (Graphic Processing Unit) and memory.
The graphics card alone can be considered as a small PC dedicated to graphics applications, independent of the rest of the PC, the only links being the information transferrred through the port and power cable.
Choosing a card is made accordingly to your needs and also your budget:
For desktop applications, an integrated chip or a low-end graphics card.
For multimedia applications, a graphics card that can play the desired video format is imperative;
For 3D video games, a more powerful graphics card will be required;
For professional (3D graphics) a professional graphic cardis essential.
Structure of a graphics card
The key component that will determine the performance graphics card is the GPU:
A modern GPU is based on different computing units:
Stream processors (SP:Stream Processors), performing the majority of the calculations on the pixels,
Texturing units (Texturing Units, TU), responsible for image textures,
Raster Units (ROPs), responsible mainly for anti-aliasing.
The most important are stream processors: the higher the number of stream processors is important, the GPU will be more powerful (for a given architecture).
The trade reference of the graphic card is linked to the GPU.
To enable the GPU to store its calculations, there is the memory:
512 MB is sufficient for graphics input for low end computing.
1GB are available for mid-range, and essential for the high end requirements;
In general, the more you expect from high resolution and filtering enabled, it takes more memory.
There are several types of Memory:
G-DDR2, G-DDR3, G-DDR4 or G-DDR5 the higher the number, the more memory is fast. This standard is of no reference to the RAM used for your PC: you can have a PC uusing DDR2 and a graphics card DDR5.
The higher, the card is more powerful.
Finally, to connect the GPU and memory, there is the memory bus.
The width of this bus is important: it may be 64, 128, 256, 384 and 512 bits:
A larger bus provide higher transfer rate between the GPU and memory are fast.
Note that: If you consider 2 graphics card sporting the same GPU, but one possess a 128 bits memory bus and other boast a 256 bits, the latter will be more powerful.
For playback of different video formats, the complete decoding of the format by the graphics card is the following:
MPEG-2: all ATI X series 1000 and beyond, all GeForce 7000 series and beyond are able to perform.
MPEG4/H.264: all ATI HD 2000 series (except HD 2900) and beyond, all GeForce 8000 series (except old 8800) and beyond are able to perform.
VC-1: all ATI HD 3000 and all GeForce 9000 series (except 9600 GT) are able to perform.
MPEG-2 is commonly used as format for standard DVD, the MPEG-4/H.264 and VC-1 concern the Microsoft HD DVD and Blue Ray.
Tips before buying graphics card
The equipment offered in the following paragraphs are intended for a new PC:
If you want to change the graphics card on an existing PC, you must pay attention to different compatibility constraints, including size, power and CPU, please read: Upgrade your PC
Be cautious about the pitfalls realted to memory standards:
Size: A graphics card with lots of RAM is useless if the GPU is not powerful: for example, it is unnecessary to have a 1GB ATI HD 4670 or HD 5670 or nVidia 9500 GT, a GT 220 or GT240.
Type: various types of memory are sometimes offered for the same GPU: G-DDR2, G-DDR3 memory and sometimes the G-DDR5. For example for the GT 240, some have the 1700MHz DDR5 (recommended), but others have the 900Mhz G-DDR3.