Radeon HD 2900 XTX (Cont’d)

On Figure 4 you can have a look on the architecture of Radeon HD 2900 XT texture unit, which supports textures up to 8192 x 8192. This chip features four texture units, each one with eight texture address processors (32 total), 20 texture samplers (80 total) and four texture filter units (16 total). There is also a vertex cache, a L1 texture cache and a 256 KB L2 texture cache.

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Figure 4: Texture unit.

On Figure 5 you can see the details of the rendering unit, which can process up to 32 pixels per clock on the depth/stencil test. Radeon HD 2900 XT has four of these units.

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Figure 5: Rendering unit.

It continues using the memory ring configuration that was introduced on the X1000 series, but now using a fully distributed design instead of a “crossbar switch”. It uses a 1024-bit memory ring, using two separated 512-bit busses, one for reads and another for writes. Another difference is that now PCI Express bus is a client of the memory ring. As already mentioned, Radeon HD 2900 XT uses a 512-bit memory interface, which is achieved by using eight 64-bit memory channels – each channel is connected to a different memory chip.

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Figure 6: Memory interface.

On Figure 7 you can see ATI Radeon HD 2900 XT. One important thing about its installation is that it uses two auxiliary PCI Express power connectors: one regular 6-pin auxiliary PCI Express power connector and a new 8-pin auxiliary PCI Express defined by the new PCI Express 2.0 standard. You have to pay close attention because this new connector resembles the EPS12V power connector available on several power supplies, but the polarity is reversed, i.e. where in the EPS12V connector is ground on the new 8-pin auxiliary PCI Express power connector is +12 V and vice-versa. If you force an EPS12V connector into the 8-pin power connector found on this video card you may burn it (we hope the power supply short-circuit protection can save your day if this happens).

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Figure 7: ATI Radeon HD 2900 XT.

Because it is still manufactured using the 80 nm process it has a typical power consumption of 215 W. AMD recommends at least a 500 W power supply for this baby (750 W if in CrossFire configuration) – however AMD certified some 400 W units to be used with this new video card. A list of certified power supplies can be found here.

Pricing is not bad at all: Radeon HD 2900 XT will reach the market with a suggested price of USD 399.

Below you can find a summary on Radeon HD 2900 XT.

Model	Clock	Memory Clock	Memory Interface	Memory Configuration	Memory Transfer Rate	Streaming Processors	Suggested Price
Radeon HD 2900 XT	740 MHz	1.65 GHz (825 MHz x 2)	512-bit	512 MB GDDR3	105.6 GB/s	320	USD 399