Special mojo?
X2 Numbers
Overall numbers are bewilderingly high. 2.4TFLOPS of math calculation; 60Gtexels/s of bilinear filtering; and, as you know, 230GB/s of combined memory bandwidth - comfortably higher than any single card that's come before.
Assuming that the motherboard supports AMD CrossFireX, another card can be installed and four-GPU rendering, which is nice.
Power-consumption figures were a concern with the engineering-model design, and AMD has managed to lower maximum TDP to 289W for the dual-GPU board, which is about 50W higher than a stock-clocked GeForce GTX 280. We're impressed by the figure, given that the framebuffer has increased, and users looking at the card should have PSUs potent enough to provide the necessary 12V juice.
We heard rumours that AMD was to bring some additional mojo to the X2 variant, and we now know them to be true.
The following slide was taken from a presentation given at a CTO Summit in Reykjavik, Iceland, just last week.
AMD refers to the inter-GPU communication ability as CrossFireX SidePort, and it's a feature that, as the name suggests, offer high-bandwidth - bi-directional 5GB/s - transfers from GPU to GPU, should they be required. We were informed that the feature will not be enabled until a later date, though.
On launch day, we expect the 2GB Radeon HD 4870 X2 to etail for around £330, including VAT, in the UK, €400 in most of Europe, and $549 (US) in the States. Interestingly, the price is commensurately lower than purchasing two Radeon HD 4870 1GB cards (£200 each), and is around £50 dearer than a stock-clocked GeForce GTX 280.
We will see AMD's board partners release their designs in a month or so. Apart from the usual differentiation by means of increasing frequencies and changing the cooler to an aftermarket model, some may opt for just 1GB of on-board GDDR5 memory, thereby reducing the market pricing a touch.
We wonder just how much money AMD and its partners are making on the Radeon HD 4870 X2 2GB, because the BOM (bill of material) cost for 2GB of 3.6GHz-rated GDDR5 cannot be cheap, but it's a problem for AMD to worry about, really.
AMD Radeon HD 4850 X2
AMD's dual-GPU (Gemini) plans don't stop just there, though, and it will release another SKU based on the RV770. This time, however, two Radeon HD 4850 1GB cards, clocked in at single-GPU speeds, will be placed on to the PCB, and the Radeon HD 4850 X2 2GB is just what you'd expect it to be.
The frequencies remain the same - 625/625/1,986MHz - and the reference design calls for a 2GB framebuffer. It'll arrive with an etail cost of around £250. We expect partners to release custom models, probably with a total 1GB on-board framebuffer, for slightly less, although no concrete timeframe has been provided by AMD.
We imagine that AMD will be pitching it directly against NVIDIA's GeForce GTX 280, with respect to performance, and we're interested to see how partners approach custom-cooled versions.
Summary
AMD's goal in designing the Radeon HD 4870 X2 2GB card was to have the fastest single-PCB graphics card around. If the on-paper specifications are an accurate predictor of performance then it's already won, but only validation via our new benchmarking suite will endorse or contradict the observation.
