Architecture

Radeon X1800 family architecture can be seen in Figure 2.

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Figure 2: Radeon X1800 family architecture.

In summary it has:

• 16 pixel shaders processors;
• 8 vertex shaders processors;
• 16 texture address units;
• 16 texture units;
• 16 render back-end units;
• 16 z compare units.

In Figure 3, you can see how a pixel shader unit looks like inside.

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Figure 3: Inside a Radeon X1800 pixel shader unit.

Chips from Radeon X1800 family use a 512-bit ring bus memory controller. Actually this controller uses two separated 256-bit datapaths, running in opposite directions. The memory controller architecture can be seen in Figure 4. Obviously the idea behind enhancing the memory controller is to make it faster to deliver data. It does that by prioritizing memory requests according to the client that asked for it. According to ATI, this change in architecture benefits basically high-bandwidth situations, like when you have your video settings at resolutions from 1600 x 1200 up, anti-aliasing at 4x  and up and anisotropic filtering at 8x and up.

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Figure 4: Ring bus memory controller.

Models

Two Radeon X1800 models were announced: Radeon X1800 XT (formerly known by its codename, R520) and Radeon X1800 XL. While Radeon X1800 XL is being launched today, Radeon X1800 XT will be only released on November 5th, 2005.

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Figure 5: Radeon X1800 XT.

The main features for these chips are shown in the table below.

Model	Clock	Memory Clock	Suggested Price	Availability
Radeon X1800 XT	625 MHz	1.5 GHz	USD 499 (256 MB) and USD 549 (512 MB)	Nov 05th, 2005
Radeon X1800 XL	500 MHz	1 GHz	USD 449 (256 MB)	Oct 05th, 2005