Sapphire Radeon HD 4850 X2 2G Review :: Features

08-28-2009 · Category: Hardware - Video Cards

By Benjamin Sun
  • 2x 956 million transistors on 55nm fabrication process
  • PCI Express 2.0 x16 bus interface
  • 2x256-bit GDDR3 memory interface memory interface
  • Microsoft® DirectX® 10.1 support
  • Shader Model 4.1
  • 32-bit floating point texture filtering
  • Indexed cube map arrays
  • Independent blend modes per render target
  • Pixel coverage sample masking
  • Read/write multi-sample surfaces with shaders
  • Gather4 texture fetching
  • Unified Superscalar Shader Architecture
  • 2x800 stream processing units
  • Dynamic load balancing and resource allocation for vertex, geometry, and pixel shaders
  • Common instruction set and texture unit access supported for all types of shaders
  • Dedicated branch execution units and texture address processors
  • 128-bit floating point precision for all operations
  • Command processor for reduced CPU overhead
  • Shader instruction and constant caches
  • Up to 160 texture fetches per clock cycle
  • Up to 128 textures per pixel
  • Fully associative multi-level texture cache design
  • DXTC and 3Dc+ texture compression
  • High resolution texture support (up to 8192 x 8192)
  • Fully associative texture Z/stencil cache designs
  • Double-sided hierarchical Z/stencil buffer
  • Re-Z, and Z Range optimization
  • Lossless Z & stencil compression (up to 128:1)
  • Lossless color compression (up to 8:1)
  • Up to 8 render targets (MRTs) with anti-aliasing
  • Accelerated physics processing
  • Dynamic Geometry Acceleration
  • High performance vertex cache
  • Programmable tessellation unit
  • Accelerated geometry shader path for geometry amplification
  • Memory read/write cache for improved stream output performance
  • Anti-aliasing features
  • Multi-sample anti-aliasing (2, 4, or 8 samples per pixel)
  • Up to 24x Custom Filter Anti-Aliasing (CFAA) for improved quality
  • Adaptive super-sampling and multi-sampling
  • Gamma correct
  • Super AA (ATI CrossFireX™ configurations only)
  • All anti-aliasing features compatible with HDR rendering
  • Texture filtering features
  • 2x/4x/8x/16x high quality adaptive anisotropic filtering modes (up to 128 taps per pixel)
  • 128-bit floating point HDR texture filtering
  • sRGB filtering (gamma/degamma)
  • Percentage Closer Filtering (PCF)
  • Depth & stencil texture (DST) format support
  • Shared exponent HDR (RGBE 9:9:9:5) texture format support
  • OpenGL 3.1 support
  • ATI Avivo™ HD Video and Display Platform6
  • Unified Video Decoder 2 (UVD 2) for H.264/AVC, VC-1, and MPEG-2 video formats
  • High definition (HD) playback of Blu-ray and HD DVD video
  • Dual stream (HD+SD) playback support
  • DirectX Video Acceleration 1.0 & 2.0 support
  • Support for BD-Live certified applications
  • Hardware DivX and MPEG-1 video decode acceleration
  • Accelerated video transcoding & encoding for H.264 and MPEG-2 formats
  • ATI Avivo Video Post Processor6
  • Color space conversion
  • Chroma subsampling format conversion
  • Horizontal and vertical scaling
  • Gamma correction
  • Advanced vector adaptive per-pixel de-interlacing
  • De-blocking and noise reduction filtering
  • Detail enhancement
  • Color vibrance and flesh tone correction
  • Inverse telecine (2:2 and 3:2 pull-down correction)
  • Bad edit correction
  • Enhanced DVD upscaling (SD to HD)
  • Automatic dynamic contrast adjustment
  • Two independent display controllers
  • Drive two displays simultaneously with independent resolutions, refresh rates, color controls and video overlays for each display
  • Full 30-bit display processing
  • Programmable piecewise linear gamma correction, color correction, and color space conversion
  • Spatial/temporal dithering provides 30-bit color quality on 24-bit and 18-bit displays
  • High quality pre- and post-scaling engines, with underscan support for all display outputs
  • Content-adaptive de-flicker filtering for interlaced displays
  • Fast, glitch-free mode switching
  • Hardware cursor
  • Two integrated dual-link DVI display outputs
  • Each supports 18-, 24-, and 30-bit digital displays at all resolutions up to 1920x1200 (single-link DVI) or 2560x1600 (dual-link DVI)2
  • o Each includes a dual-link HDCP encoder with on-chip key storage for high resolution playback of protected content3
  • Two integrated 400 MHz 30-bit RAMDACs
  • Each supports analog displays connected by VGA at all resolutions up to 2048x15362
  • DisplayPort output support
  • 24- and 30-bit displays at all resolutions up to 2560x16002
  • HDMI output support
  • All display resolutions up to 1920x10802
  • Integrated HD audio controller with support for stereo and multi-channel (up to 7.1) audio formats, including AC-3, AAC, DTS, DTS-HD & Dolby True-HD4, enabling a plug-and-play audio solution over HDMI
  • Integrated AMD Xilleon™ HDTV encoder
  • Provides high quality analog TV output (component/S-video/composite)
  • Supports SDTV and HDTV resolutions
  • Underscan and overscan compensation
  • Seamless integration of pixel shaders with video in real time
  • VGA mode support on all display outputs
  • ATI PowerPlay™ Technology5
  • Advanced power management technology for optimal performance and power savings
  • Performance-on-Demand
  • Constantly monitors GPU activity, dynamically adjusting clocks and voltage based on user scenario
  • Clock and memory speed throttling
  • Voltage switching
  • Dynamic clock gating
  • Central thermal management – on-chip sensor monitors GPU temperature and triggers thermal actions as required
  • ATI CrossFireX™ Multi-GPU Technology
  • Scale up rendering performance and image quality with two, three, or four GPUs
  • Integrated compositing engine
  • High performance dual channel bridge interconnect1

Brand Name Sapphire
Part Number HD 4850 X2 2G GDDR3 PCIE
Graphics Chip RV770 Pro
Core clock 625MHz
Shader Clock 625
SPs 2x800
Fabrication Process 55nm
Transistors 2x 956 million
Memory clock 1986MHz
Memory bus 2x 256-bit
Memory bandwidth 2x 63.6GB/second
Memory Size 2x1024MB
ROPs 16
Texture Filtering Units 40
Texture Filtering Rate 25.0 Gigatexels/second
HDCP Support Yes
HDMI Support Yes (via adapter)
Connectors Quad DVI, S-video
RAMDACs 400MHz
Bus PCI Express 2.0
Form Factor Dual Slot
Power Connectors 6-pin, 8-pin

Sapphire's new card has two HD 4850 chips. Each chip has 956 million transistors on TSMC's 55nm fabrication process. Each HD 4850 chip has 800 Stream Processors which are actually 160 5D cores. The HD 4850 is capable of 1 TeraFLOPs of computing power, meaning that the card is one of the first to hit that plateau.

The clock speed of the Sapphire card is 650MHz for the core clock speed, which is a far cry from the 850MHz clock speed of the HD 4890 or the 750MHz clock speed of the HD 4870 this card was designed as a stablemate to. The memory clock is at 1GHz. The card has a 256-bit memory interface using GDDR3 memory meaning that the memory bandwidth of the card is 128GB in total (64GB for each chip).

ATI's current lineup consists of cards that support DirectX 10.1 from the high-end to the integrated lineup. DirectX 10.1 is a modest improvement over 10.0, with image quality improvements, and the ability to parallax cube mapping on the GPU. DirectX 11 is the next step and it will be released in conjunction with Microsoft Windows 7. To support DX 11, you need to fully support DX 10.1.

One of the big things with DirectX 11 is the Compute Shader. This allows the graphics card to be used as a computing device. The Radeon HD 4850 x2 can use the CS 4.1 framework with DirectX 11 to speed up post-processing effects and imaging. There are three frameworks in DirectX 11: CS 4.0 (Most NVIDIA cards), CS 4.1 (ATI cards), and CS 5.0 (upcoming DirectX 11 compliant video cards).

The HD 4850 has a hardware tessellator. A Tessellator has several key advantages over normal geometry shading. The first advantage is the ability to reduce the memory footprint and bandwidth consumption. The second advantage is the bandwidth usage is improved due to the lower resolution model being sent to the GPU instead of the higher polygon model. Tessellation also improves the scalability. On ATI's Froblin demo, the frog has a low resolution footprint of 100KB with 5160 face and a displacement map of 10MB. The high resolution model has 15 million faces, a footprint of 270MB for the Vertex Buffer and 180MB for the Index buffer.