ASUS GeForce EN8800GTX/HTDP/768M Video Card Review :: GeForce 8800 Texturing and Filtering

11-09-2006 · Category: Hardware - Video Cards

By Benjamin Sun

The GeForce 8800GTX has fully decoupled texturing units from the stream processors. The 8800GTX can deliver up to 64 pixels per clock of raw texture filtering horsepower, (versus the 24 on the GeForce 7900 GTX), 32 Pixels per clock of texture addressing, 32 pixels per clock of 2x anisotropic filtering, and 32-bilinear filtered pixels per clock. What this means is that bilinear anisotropic filtering is almost free on the GeForce 8 (nothing is free in 3D). FP16 bilinear filtering output is 32 pixels per clock, and FP16 2:1 AF is done at 16 pixels per clock.

Texture units and streaming processors

ASUS GeForce EN8800GTX/HTDP/768M Video Card Review

The texture units are clocked at 575 MHz. With 32 pixels per clock of bilinear filtered texels that gives a texel fill rate of 18.4 Gigatexels a second which is the standard way to derive texel fill rate. However, when 2:1 bilinear anisotropic filtering is applied, two bilinear texels are used, giving the card an effective 38.4 gigatexel fill rate. Ugh, NVIDIA's math isn't important to me, as I like to deal with real numbers.

The GeForce 8800GTX can output 24 pixels (ROPs) in a single clock with color and Z-processing. The 24 ROPs are divided into 6 partitions of 4 (16 subpixels samples). There is a new mode called Z-only processing that allows 192 samples per clock. If 4x MSAA is applied then 48 Pixels Z-only processing is possible. Again, ugh, in terms of pure pixel fillrate, the 8800GTX can output 24x575MHz=13.2 Gigapixels a second theoretical, more than enough to fill a 2560x1600 screen many times.

The memory architecture on the 8800GTX is split into 6 partitions of 64-bit memory. This matches well with the 24 outputted pixels per clock as its one memory partition per quad of outputted pixels. Graphics cards have been stuck on the 256-bit memory bus since the RADEON 9700 Pro and the GeForce 5900 series. The 8800GTX is the first card on the commercial market to sport a 384-bit memory bus. ASUS clocked the memory on their 8800GTX at 900MHz, 1.8GHz effective, the same as the reference clock. The memory bandwidth on the 8800GTX is 86.4GB/second.