Palit Radeon HD 4870 X2 Video Card Review :: ATI Radeon HD 4870 X2 Features

08-12-2008 · Category: Hardware - Video Cards

By Doc Overclock

Palit Radeon HD 4870 X2 Video Card Review

  • 55 nanometer process
  • 1600 Stream Processors
  • 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
  • Shader instruction and constant caches
  • Up to 320 texture fetches per clock cycle
  • Fully associative multi-level texture cache design
  • DXTC and 3Dc+ texture compression
  • High resolution texture support (up to 8192x8192)
  • Double sided
  • 230GB/second memory bandwidth
  • 2GB GDDR5 memory
  • PCI Express Generation 2 Interconnect
  • 24x Custom Filter Anti-Aliasing
  • 16x AF
  • DirectX 10.1
  • Shader Model 4.1
  • 32-bit floating point texture filtering
  • Indexed cube map arraus
  • Independent blend modes per render target
  • Pixel coverage sample maxing
  • Read/write multi-sample surfaces with shaders
  • Gather4 texture fetching
  • 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
  • CrossfireX
  • PCI Express 2.0
  • Unified Video Decoder 32
  • Upscale beyond 1080p
  • On-chip HDCP
  • HDMI
  • PowerPlay
  • 956 million transistors x2
  • 256-bit GDDR5x2 memory interface

Palit Radeon HD 4870 X2 Video Card Review
Brand NamePalit
Part NumberHD 4870 X2
Graphics ChipR700
Core clock750MHz
Shader Clock750MHz
Fabrication Process55 nm
Transistors956 Million
Memory clock(3.6GHz effective)
Memory Interface256-bit x2
Memory bandwidth230GB/second
Memory Size2048MB
Texture Filtering Units64
Texture Filtering Rate40.6 Gigatexels/second
HDCP SupportYes
HDMI SupportYes (via adapter)
Connectors2x Dual-Link DVI, TV-Out
Bus PCI Express 2.0
Form FactorDual Slot
Power Connectors 2x 6-pin

Hereís a chart comparing the GTX260, GTX280, HD4870 and HD4850 in terms of features and price online as of 8/11/2008:

GTX260GTX280HD4850HD 4870HD 4870 X2
Transistors1.4 billion1.4 billion956 million956 million1.912 billion
Memory bus448-bit512-bit256-bit256-bit256-bit x2
Memory896MB1024MB512MB512MB1024MB x2
Memory bandwidth112GB/second141GB/second64GB/second115GB/Second230GB/second
Texture Fillrate40 Gigatexels/second48.2 Gigatexels/second20Gigatexels/second20.3Gigatexels/second40.6 Gigatexels/second

The Palit HD 4870X2 is based upon ATIís HD4870 X2 reference design. The card is based around two RV770XT chips on the same PCB (Printed Circuit Board). The HD 4870 X2 is based on TSMCís second generation 55 nanometer process with each 4870 X2 chip having 956 million transistors. Two of the chips have 1.912 Billion transistors, the largest amount of transistors on a video card available today. The die size of each chip is 256mm2.

Each HD 4870 chip has a 256-bit memory interface and uses 1GB of GDDR5 memory for the Framebuffer, meaning that the HD 4870 X2 has 2GB of memory. The total memory bandwidth on the HD 4870 X2 card is 230GB/second, or exactly doubles that of a single HD 4870 card which had a total of 115.2GB/second. The memory clockspeed on the HD 4870 X2 is 900MHz or 3.6GHz effective due to the way GDDR5 works.

The clock speed on the Palit HD 4870 X2 is 750MHz for the core, the same as found on the HD 4870 reference card. The HD 4870 X2 has 800 Stream Processors per chip or 1600 total SPs. In way of comparison the GTX280 from NVIDIA has 240 SPs but the way they operate is different and should not be counted the same way. The fillrate of the HD 4870 X2 is 8.1 Gigapixels/second and a texture fillrate of 20.3 Gigatexels/second.

ATI has been touting the efficiency of their HD4xxx series of cards as being over 2.8x that of the GTX280 in terms of performance per watt. The HD 4870 X2 has a maximum power draw of 248W. The GTX280 from NVIDIA has a total wattage maximum of 236W, but the HD 4870 X2 is two chips, providing much more performance for nearly the same power draw. ATI touts DirectX 10.1 functionality with their cards since the HD 3870 launch last year. Today there are no video games on the PC market with support for DirectX 10.1 except for Assassinís Creed and the developers of that game removed that feature from the game with the first patch due to issues. I wonít go into the marketing speak except to note that the features like cube map indexing and improvements to anti-aliasing are cool but not the showstopping features that would bring a new generation of games like DirectX 10.0 did.

The R7xx series has a programmable tessellation unit. Tesselation allows complex geometry from a smaller set of triangles. The HD 4870 X2 has massive computing power on a single card. The 4870 chip is capable of 1.2 TeraFLOPs of computing power, meaning that two of the cards will be capable of 2.4 TeraFLOPS of computing power, compared to the 933 GigaFLOPS on the NVIDIA GeForce GTX280 cards. That means it is possible to have nearly 5 TeraFLOPS on two HD 4870 X2 cards.

One of the new features of the HD 4870 X2 card is the bridge chip that connects the video chips to each other and to the system. ATI states that the new chip is equivalent to a PCI Express 2.0 path. It provides 16 lanes to each RV770 chip and 16 to the system. The bandwidth is between the bridge chip and the system is 5GB/second double that of the previous generation found on the HD 3870 X2 card which had two HD 3870 chips on it. This is the most obvious advancement for ATI to take at this time in any case.

ATI has been at the forefront of anti-aliasing in recent years. Today, their cards can do 8-sample MSAA. They use a near random sample pattern, meaning that the best image quality in anti-aliasing can be achieved through the sample pattern. They have the ability to use a Custom Filter to their AA that improves the image quality to up to 24x quality in certain situations where the edges meet. CrossfireX is ATIís branding on their multi-GPU solution. The HD 4870 X2 card can be paired with a like card from the various manufacturers and deliver almost double the performance in situations where the graphics card is not the limiting factor. To enable CrossfireX you need two cards, an ATI or Intel motherboard that has two PCI Express x16 Generation 2.0 slots and a Crossfire bridge for each card.