www.cpuplanet.com/features/article.php/2117941
March 19, 2003 Is It Worth It?AGP technology is certainly light-years ahead of the old PCI bus, and the newest AGP 8X graphics cards from Nvidia, ATI, and others bring plenty of benefits to the table. But the new spec does bring with it some inherent challenges. The most obvious is public perception, and the natural inclination to associate AGP 8X as being twice as fast as AGP 4X. This is actually far from the truth, as AGP 8X bus speed is not strictly a performance metric. Any real-world speed benefit depends on the application or game used, the design of the graphics card itself, and even the design of the overall platform. A prominent example is current 3D cards' handling of texture memory. Intel has long promoted AGP as a method of offloading texture graphics to system memory, thereby saving on more costly onboard (meaning on-graphics-board) buffer memory. This is largely a fallacy. Early on, there were several 4MB and 8MB AGP cards that simply didn't provide the juice to power 3D applications. Even with the latest dual-channel DDR platforms, general-purpose system memory is just too slow compared to a high-end video card's memory. This is magnified on a card like ATI's newest Radeon 9800 Pro, which features a 256-bit interface to 680MHz DDR memory, along with specialized memory-optimization features and high-end color and z-compression algorithms that no PC platform can even approach. As graphics technology improved, memory storage and operations have almost totally moved from the motherboard to the graphics card (with the obvious exception of low-priced desktops and laptops using integrated-graphics chipsets). Even today's entry-level 3D cards feature 64MB of onboard DDR memory, while higher-end products ship with 128MB standard and 256MB configurations are on the horizon. While higher AGP speeds do benefit integrated chipsets such as Intel's 845G and GE, whose only data source is system memory, not even AGP 8X with its 2.1GB/sec bandwidth can hold a candle to the 8GB/sec memory bandwidth of Nvidia's current entry-level GeForce4 MX 440, let alone the 21.8GB/sec of the top-end Radeon 9800 Pro. That is not to say higher-speed AGP interfaces don't come in handy, but only that their impact has been muted by the more card-centric features of today's graphics accelerators. Other forms of data (with less intensive requirements) do make use of the AGP bus, and depending on the graphics design, vertex, triangle, or other 3D data are routinely stored in system memory and flow back and forth across the AGP bus. AGP 8X PerformanceIn terms of AGP performance numbers, the vast majority of current games and applications show no real advantage on the AGP 8X bus, when compared to AGP 4X. In most cases, the AGP 8X bus is not even a consideration (2D Windows applications) or is not the limiting performance factor (3D games or applications). That said, there is some evidence that future 3D development may change this scenario. For example, one of today's most demanding 3D games, Unreal Tournament 2003, shows very noticeable AGP 8X framerate gains (in the neighborhood of 15 to 30 percent depending on the graphics card). Game guru John Carmack has been touting AGP 8X as a virtual requirement for the long-awaited Doom III. Another important factor is the speed of the graphics card itself, as you will see more noticeable AGP 8X gains from a top-end card than a value model. It's regrettable that AGP 8X seems to be turning into a "checkmark" item, reassuring buyers that their purchases are up-to-date even where it's actually irrelevant; from our testing, the upper middle (say Nvidia's GeForce4 Ti) segment is the point where AGP 8X starts making sense, or where you'll notice higher performance results with AGP 8X enabled. That said, there's no reason not to buy a lower-end AGP 8X card, just as long as you don't expect a radical performance jump. But if you're not avid to upgrade this year, there might be some wisdom in saving to buy an all-new system with PCI Express -- and Serial ATA, IEEE 1394b, and other advances -- in 2004. |
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