One of the most used words when describing a 3D Accelerator is the word fill-rate. Even more right now there seems to be a battle... the battle for the highest fill-rate. But is everybody in this battle using the same definition of fill-rate, and why do some companies use Mtexels and others Mpixels to define their fill-rate ? Even more : does this "Fill-rate"-number have a real meaning ?

Lets have a look at some fill-rate related claims:

"ATI introduces next-generation RAGE 128 GL graphics chip delivering world's best performance and features to the high-performance PC Market ... First to break the 1 Gigatexel per second texturing barrier with SuperScalar rendering engine and single-pass multi-texturing ...
- from an ATI Press Release.

"... The 143MHz Voodoo3 2000 AGP and PCI boards are expected to generate up to 6 million triangles and 286 Megatexels per second at resolutions of up to 2,048 by 1,536 pixels ... The 166MHz Voodoo3 3000 AGP board is expected to generate 7 million triangles and 333 Megatexels per second at resolutions of up to 2,048 by 1,536 pixels ... The 183MHz Voodoo3 3500 AGP board is expected to deliver up to 8 million triangles and 366 Megatexels per second at resolutions of up to 2,048 by 1,536 pixels..." 
- From a 3Dfx Press Release.

"... 90 Mpixels/sec sustained fill rate for dual textures bi-linear filtered polygons, with LOD MIP-mapping, Z-buffering,alpha-blending and fogging enabled ..." 
- From another 3Dfx Press Release.

"... The Viper V550 features NVIDIA's RIVA TNT processor, the first single-chip 128-bit 3D processor able to process two pixels per clock cycle to provide true single-pass multi-texturing for exceptional 3D realism. Scaleable, true-color resolutions of up to 1920x1200, ultra-fast fill rates up to 250 million pixels- per- second and an enhanced dual-pixel 32-bit color pipeline all contribute to the Viper V550's phenomenal performance and visual quality output with processing power matching that of the Intel Pentium II processor..." 
- From a Diamond MultiMedia Press Release

"... PowerVR Second-Generation products will deliver  1.2 m polygons/second and a fill rate of 120 megapixels/second equivalent..." 
- From a NEC / VDO / PowerVR Press Release.

I will try to define and explain the various types of Fill-rate that are being used today, that way you will be able to figure out what all these numbers really mean.