The other major change is the move to GDDR4 memory. Interestingly, Nvidia was the first company that manufactured a video card equipped with DDR on its GeForce 256 DDR, and DDR3 on the GeForce FX 5700 Ultra. ATI has taken the lead with new memory integration and presents GDDR4 on its Radeon X1950 graphics cards. By utilizing this new memory type, ATI becomes the first graphics company to break the Gigahertz barrier for graphic memories operating at 1 GHz (1,000 MHz, which is effectively 2 GHz DDR).
GDDR4 is built on a smaller fabrication process and will natively consume less energy per clock than GDDR3 memory modules. Smaller process continues to elevate the frequency speed threshold as the electrical gates are smaller and can switch faster. ATI claims that the power savings from the incorporation of new modules will be virtually nullified since the clock speeds are so much faster. Power consumption should therefore remain the same, but the memory bandwidth and performance should increase.
With the other SDRAM specifications, GDDR4 is also an open standard. Many companies participated in the design project, including ATI and Nvidia, as well as memory manufacturers such as Hynix, Infineon, Micron and Samsung. While it is an open standard that companies can choose to produce, there are still a limited number of suppliers at the moment. This should ramp up and we could see the price of GDDR4 start to come down. For this reason, ATI has only implemented this technology into its high-end products.
The advantage of higher clock frequencies means that the amount of data that can flow from the modules into and out from the 512 bit wide ring bus can be expanded. While the external bus to the modules remains at 256 bits wide and module densities remain the same as GDDR3 (512 Mb or 32Mb x 32), the maximum theoretical bandwidth of the GDDR4 memories is now 64 GB/s. That is a 25% bandwidth increase or 13 GB/s over DDR3 at 800 MHz. According to Joe Macri, senior director of circuit technologies at ATI, in the near future these memories could be pushed up to 1.35 GHz, and Samsung has stated that it could be pushed up to 1.5 GHz.
The latest innovations in GDDR come from tweaks such as lower voltage requirements, data bus inversion, widened to a 8-bit data prefetch (versus previous 4-bit prefetch), and a longer fixed burst lengths allows for a better signal in during transmissions and mean power savings. We will continue this discussion in another article but wanted to get the highlights out for the launch.