X-bit labs

ATI RADEON X700 XT: Architecture Preview (page 5)

Category: Video

by Alexey Stepin , Tim Tscheblockov, Anton Shilov

[ 09/21/2004 | 04:54 AM ]

RADEON X700 XT: Theoretical Tests

We used two platforms with PCI Express and AGP graphics buses, respectively.

The PCI Express platform:

• Intel Pentium 4 560 (Socket 775, 3.60GHz, 1MB L2 cache);
• Intel Desktop Board D925CXC;
• 2x512MB Micron Technology PC2-4300 DDR2-533MHz SDRAM;
• Samsung SpinPoint SP0812C HDD (SerialATA-150, 8MB buffer);
• Creative SoundBlaster Audigy2 sound card;
• Microsoft Windows XP Pro with Service Pack 2 and DirectX 9.0c.

The AGP platform:

• Athlon 64 3400+ CPU (2.20GHz, 1MB L2 cache);
• ASUS K8V Deluxe mainboard;
• 2x512MB OCZ PC3200 Platinum EB DDR SDRAM (CL2.5-3-2-8);
• Seagate 7200.7 HDD (SerialATA-150, 8MB buffer);
• Creative SoundBlaster Audigy2 sound card;
• Microsoft Windows XP Pro with Service Pack 2 and DirectX 9.0c;
• ATI Catalyst 4.8, NVIDIA ForceWare 61.77 (version 60.85 for 3DMark03).

To avoid confusing you, we mark the graphics cards tested on the AMD64 platform (RADEON X800 PRO and RADEON 9800 XT) with the asterix sign (*).

Texturing Speed

Marko Dolenc’s Fillrate Tester opens the cycle of our synthetic tests.

The RADEON X700 XT quite naturally does multi-texturing slower than the X800 PRO that has 12 pixel pipelines against the X700 XT’s 8 pipes. More discouraging is how the new GPU compares to the NVIDIA GeForce 6600 GT: outperforming the rival with no textures and being equal to it at single-texturing, the X700 XT turns in much worse performance when rendering more textures. These two graphics cards – ATI RADEON X700 XT and NVIDIA GeForce 6600 GT – have the same number of pixel pipelines and similar GPU clock rates, but the former is two times less efficient than the latter at rendering 4 textures!

The next table shows you the efficiency coefficients of the graphics cards, i.e. the ratios of the real performance to the maximum theoretical speed at simple texturing:

The cards behave quite differently: the efficiency of the NVIDIA GeForce 6600 GT is steadily increasing to reach as high as almost 87%, while the ATI RADEON X700 XT is less successful – only 48-57% when rendering from 1 to 4 textures. Such a low texturing efficiency may be the result of several factors working together, among which we think the most crucial are the insufficient bandwidth of the 128-bit memory bus or a too severe reduction of the size of the texture caches when the X800 was converted and truncated all around to become the X700.

The RADEON X700 XT takes a good start here, even leaving behind the RADEON X800 PRO with no textures thanks to the higher clock rate, but rolls back to the last position at rendering two or more textures.

Everything looks normal when we disable color writes: the RADEON X700 XT makes a good use of its high clock rate to outperform the RADEON 9800 XT, but of course loses to the 12-pipelined RADEON X800 PRO and to the NVIDIA GeForce 6600 GT which can write down as many as 16 Z-values per clock.