An interview with ATI - Dave Baumann

Back to the ATI Radeon HD 4890 thus using a 256-bit memory interface. The enthusiast consumers out there will just love the new tweakability of the card. We are seeing some boards manage 1 GHz on the core frequency and surpass 4000 MHz (effective) of GDDR5 memory. Focusing merely on the GPU clocks, we jump from a 750 MHz (RV770) towards a potential 850 even 900~1000 MHz ... It is very rare to see 20-25% increases in clock frequencies. What is the trick there?

There's no "trick" here, just some great engineering from the team! :

When we got RV770 back it obviously hit our targets for the products very nicely, however the overclock potential of the ASIC was limited. With the RV790, the target was to basically uncap that limit. Because we were dealing with an architecture we knew very well and a process with which we were very familiar, we were certain we could achieve much higher clocks.

Starting from this basis we took the RV770 and re-scrubbed it from a physical design point of view, with changes to timing, power distribution and also adding de-coupling capacitors to reduce noise and increase signal integrity. This effectively enabled much higher clocks from our reference configurations.

We expect a number of partner variations on our reference boards - most of our partners already had 900MHz versions available at or soon after launch and we expect to see even higher clocked models in the near future.

A reader question: I had a user question asking, what happened to Sideport (XSP)? Sideport was intended to add more interconnect bandwidth. It has been disabled ever since the release of the RV770 (X2) from day 1. We heard that "that much bandwidth is not needed". IMO... you can never have enough bandwidth really. What was going on there?

This is simply a case of our software capabilities catching up to our hardware capabilities.
When the initial design of the RV770 was taking place and concepts such as Sideport were being kicked around our ATI CrossFireX™ software wasn't in the place it is right now, so there was a much higher reliance on inter-chip communication.

While having lots of bandwidth is rarely a bad thing, the ATI CrossFireX communication bandwidth between two discrete cards is less than local bandwidth - even though Sideport doubles the inter-GPU communication bandwidth on an X2 type solution it's still not significant enough to really change the disparity in local frame buffer and inter-GPU bandwidths.

The software work that occurred in the space of time between the RV770 design and product saw significant improvements in inter-GPU communication. Internal to the driver we now have a number of "alternate frame rendering" (AFR) profiles, with many parameters that can be tweaked in order to control how the rendering behaves over multiple GPU's and reduce the inter-GPU communication as much as possible. By the time we put two RV770's on a board and started testing Sideport, the current ATI CrossFireX software capabilities delivered more than enough bandwidth, obviating the need for Sideport.

Any chances of a ATI Radeon HD 4890 X2 model anytime soon?

At this point in time we are concentrating on ATI Radeon™ HD 4890 to address a pricing gap in the market.

Currently, sales of the ATI Radeon™ HD 4870 X2 are strong as are sales of our high-end single GPU solutions, suggesting that an additional ultra-enthusiast product may not be warranted at this time.

In two lines summed up, what will be the key selling points and hardcore features of the ATI Radeon HD 4890 for the end-user?

Fantastic gaming performance, great overclocking / tweakability, enormous compute power, and support for the latest industry standards such as DirectX 10.1 as well as ATI Stream. *
There, did it in one line! :

* AMD's product warranty does not cover damages caused by overclocking, even when overclocking is enabled via AMD software.

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