|
|
|||||||||||||||||
|
ATI calls their HD 5xxx family the Evergreen family of chips. The high end is represented by the 2.15 Billion transistor Cypress chip (HD 5870, HD 5850), the performance segment by the 1.04 billion transistor Juniper chip (HD 5770, HD 5750) and later variants to be represented by chips called Redwood and Cedar. Today’s Crossfire review is on the Juniper chips (HD 5770 and HD 5750) that have the $160 and $129 markets sewn up. If you look at it from a performance/price ratio point of view two HD 5770s are less expensive than a single HD 5870 and performance should be similar. The same story is true of two HD 5750s as they are basically half a HD 5850 in terms of ROPS, TMUs and memory. I’ve covered the features of the HD 5xxx series in various other articles and as I’ve already reviewed these cards in other reviews, it’s a bit redundant to cover them again. The relevant features to this review are CrossfireX and Anti-Aliasing. First a little history lesson on Crossfire and then I’ll cover anti-aliasing. The point of this article is to show CrossfireX performance on two different pairs of cards in the form of the HD 5770 and HD 5750. So what is CrossfireX anyway? A few years ago a company called 3DFX existed and created a multiple-GPU solution in the form of two Voodoo 2 cards. This improved performance by nearly 100% over a single card and improved image quality. 3DFX was the first company to introduce multiple graphics cards for the consumer gaming space. ATI introduced Crossfire with the advent of the x800 series video cards in 2005. The first generation of Crossfire required a Master and a Slave video card, an external Crossfire cable and a Crossfire compliant motherboard with two PCIe slots. The X850XT Master card used a Silicon Image compositing chip (Sil 163 TMDS the maximum resolution of Crossfire first generation was 1600x1200 at 60Hz or 1920x1440 at 52Hz. ATI removed the limitation with the X1800 series as it required no Master card. With the advent of the X1800 series the Crossfire dongle was no longer required. What you needed to achieve this was a CrossFire Xpress 3200 motherboard and two ATI RADEON cards that communicated over the PCI Express bus. Today, ATI has implemented a bridge system much like NVIDIA’s SLI implementation. Two cards or more (Up to four) can be daisy-chained to each other improving performance over a single video card. ATI uses two methods to render with CrossfireX: Scissors, Checker board mode and Alternate Frame Rendering Mode. Scissors mode splits the frame into half with one video card rendering the top half of the image and the other rendering the bottom half of the image. Checker board has the image split into smaller squares which are assigned to different cards. Alternate Frame Rendering has the first video card render one whole frame, the second the next frame, etc. In most cases Scissors mode is the most inefficient as some parts of a rendered scene are more complex than others. AFR is most useful because the image usually doesn’t change much from one frame to the next, meaning the workload is mostly similar.  CrossfireX With the advent of the ATI HD 5xxx series, the video card has the ability to do Super Sample Anti-Aliasing on images as well as Multi-Sample Anti-Aliasing. Super Sample Anti-Aliasing basically renders a scene at a higher resolution and down-sampling the result to a lower resolution. Multisampling has the graphics chip or chips evaluate one color, stencil, etc value per pixel and supersample the depth value. The difference is that SS takes several samples inside a pixel and MS takes a sample once. ATI has implemented anti-aliasing in a myriad of ways on the HD 5xxx series and more options are available with two or more cards installed in CrossfireX mode. Custom Filter Anti-Aliasing looks at the pixels around the pixel being processed in order to calculate the final color and anti-alias the image. The HD 3xxx series and later cards use wide and narrow tent filters. The samples outside the pixel being processed are weighted linearly based upon their distance from the center of that pixel with the linear function adjusted based on the wide or narrow filter chosen. The HD 5770 and HD 5750 are capable of 8x FSAA by themselves in the normal mode. With CFAA you can improve that to 24x AA effectively. With CrossfireX enabled you can set up to 16x FSAA natively in the driver with up to 24x FSAA Narrow Tent and 32X FSAA Wide Tent available if you change the settings. The HD 5xxx series is capable of SSAA and has a tab on their drivers to enable it. Performance of the new cards should be enough to play in 8x FSAA in most games with two HD 5770s in CrossfireX mode.  No AA  8x AA SuperSampling  8x AA Multisampling  16x AA Contents:
|
|
|||||||||||||||
