ATI Radeon 64MB DDR

More of the Chip, Part II

In addition to these hardware T&L solutions, the Charisma core actually implements features of the yet to arrive DirectX 8 API. Including support for 3D textures and 4 matrix vertex skinning (used in Microsoft's upcoming Dragon Siege) ensures that the Radeon will be able to handle the next generation of games. In addition, environmental bump mapping will be supported by the Radeon. NVIDIA's current generation of cards do not support this bump mapping method, however Matrox has been using it since the G400.

With all these features, developers seem to agree: the Radeon will be the most feature rich GPU on the market today.

The Radeon has the best feature set available, with several advantages over GeForce... On paper, it is better than GeForce in almost every way except that it is limited to a maximum of two pixels per clock while GeForce can do four. This comes into play when the pixels don't do as much memory access, for example when just drawing shadow planes to the depth/stencil buffer, or when drawing in roughly front to back order and many of the later pixels depth fail, avoiding the color buffer writes.

Depending on the application and algorithm, this can be anywhere from basically no benefit when doing 32 bit blended multi-pass, dual texture rendering to nearly double the performance for 16 bit rendering with compressed textures. In any case, a similarly clocked GeForce(2) should somewhat outperform a Radeon on today's games when fill rate limited. Future games that do a significant number of rendering passes on the entire world may go back in ATI's favor if they can use the third texture unit, but I doubt it will be all that common.

The real issue is how quickly ATI can deliver fully clocked production boards, bring up stable drivers, and wring all the performance out of the hardware. This is a very different beast than the Rage128. I would definitely recommend waiting on some consumer reviews to check for teething problems before upgrading to a Radeon, but if things go well, ATI may give nvidia a serious run for their money this year.

- John Carmack, .plan update 5/17/00

In addition to the features of the Charisma core, ATI also added integrated TMDS support in the chip, making DVI-output an easy addition. This feature seems targeted mostly to ATI's strong OEM market, as ATI could not predict if any DVI models will make it to the retail stores, but one should be able to find these cards as special OEM box purchases online.

Despite the addition of some additional features that were not present at the product launch, one card spec actually took a turn for the worse. At WINHEC, ATI told us of a card that would have an impressive memory and core speed of 200 MHz. Well, as speed specs often do, ATI decreased the core and memory clock specs for the shipping Radeon. Due to what seems to be the unavailability of 5 ns DDR SDRAM, ATI was forced to take 5.5 Ns DDR SDRAM, putting the memory clock speed at 183 MHz DDR (366 MHz effective). The core speed, either due to less than expected yields or just ease, is also shipping at the 183 MHz mark. As we will see in the benchmarking section, pushing up the core really does not result in any performance increase due to extensive memory bandwidth limitations.

The 183 MHz core and memory speeds provide the Radeon with a raw fill rate of about 1.1 gigatexels per second, and 366 megapixels per second. With a drop of about 100 megatexels per second and 34 megapixels per second from the announced solution, the shipping Radeon cards are also 500 megatexels and 434 megapixels slower than the GeForce 2 GTS.

ATI is betting that this will not matter, once again due to memory bandwidth limitations. ATI claims that even if you’re using 200MHz DDR SDRAM (effectively 400MHz), you’re limited to a 300 megapixels per second fill rate at 32-bit color with a 32-bit Z-Buffer, so adding more pixel pipelines would not’t help them, which is why they focused on having three texture units per pipeline. To see if this is the truth or not, we will have to turn to the benchmarks, which are given later in this review.