VIDEO CARDS: difference between Memory Bandwith and Processing Power

[josemavicente]

Im posting this because of an article I read with quote:


QUOTE]What does this suggest? That the GeForce FX is very fast -- particularly when memory bandwidth isn’t an issue. Remember that the GeForce FX’s 128-bit memory bus runs at 500MHz, but has a maximum bandwidth of just 16GB/sec. Meanwhile, the Radeon 9700’s 256-bit memory interface accommodates 19.8GB/sec, even though it runs at just 325MHz.[/QUOTE]

Whats the difference between memory bandwith and the processor power ofthe video card? When does one matter more?[

[ski]

A video card's core speed and memory bandwidth are both important for graphics performance.
The following is a very basic explanation.

The core speed of the card's graphics chip determines the fill rate of the card.
The fill rate is the pixel/texel rendering power of the video card.
A fast fill rate equates to better performance, especially at higher resolutions where there are more pixels and texels to render.
If a card reaches its fill rate limit at a specific resolution, then it gets stuck at a specific level of performance at that resolution.

The clock speed and the data path width(bits) of the card's memory determines the maximum memory bandwidth of the card.
A higher memory bandwidth means that a greater amount of data can be
transferred from the graphics chip to the motherboard.
Memory bandwidth limitations are also like fill rate limitations, wherein the card can reach a certain performance point at a specific resolution and get stuck there.

For example, if a card has a slow core speed coupled with a high memory bandwidth, then its fill rate will be less than what the memory bandwidth can handle, and the card's performance will become 'bottlenecked' by its graphics chip.
On the other hand, if it has a fast core speed coupled with low memory bandwidth, then its fill rate will exceed what the MBW can handle, and the MBW is now the bottleneck.

And to make the issue even more complicated, the performance of certain games are more dependent on a card's core speed, while other games' performance are more MBW dependent, and some games require both a fast core speed and high MBW to achieve max performance.