AMD ATI Radeon HD 4770 512MB GDDR5 review

Page 2 - Close look at HD 4770 and RV740

Even though RV740 is a new core, it to a great extent is based on the architecture of HD 4850/4870/4890. The chip has a 128-bit interface therefore the use of GDDR5 memory is rather important. GDDR5 allows for twice as high data stream (the real 800MHz of the card are in fact effectively 3200MHz) and HD 4770 with 128-bit GDDR5 memory has overall slightly lower memory performance than HD 4850 with 256-bit GDDR3. And if we mreally must be really, really precise - the HD 4770 memory performs at exactly 51.2GB/s, while HD 4850 does that at 64GB/s. But as we will prove later that difference in performance is not crucial.

Still, it is the small changes that make the new core so good and that's why we're paying them so much attention. RV740 has 128 five way super scalar shader units or 640 scalar processors, whatever floats your boat. Ours floats better with "640 scalar processors", since shaders differ with different AMD models :)

The card has 20% less scalar processors than the HD4850 core (800), but it compensates with its higher core frequency (750MHz compared to 625MHz). Thus the texture sample rate is 24.0 GTexels/sec, while with HD 4850 it is with only 1 GTexel higher. HD 4770 outperforms HD 4850 though in pixel fillrate, it is for the first of them a 12 gigapixels per second, compared to just 10 for HD 4850. Whether that is considerably beneficial on behalf of HD 4770 is still arguable, it is however an undisputed fact :)

As for the physical characteristics of HD 4770 - with its 21cm it is one of the shortest cards in its class at this time. Its dual slot cooling is fully copper once you look under all the plastic and two additional heatpipes aid for the faster heat dispersion. The card is also provided with a 70mm fan which is pretty quiet in idle mode. The board also comes with a 6-pin PCI connector and considering that AMD claim that in normal peak HD 4770 could consume as much as 80W, and knowing that the PCI-E slot on itself can supply up to 75W, we can surely expect a good overclock potential. Predictably, we do expect to see soon new series of more energy efficient "green" cards that lack that additional power connector.

Half of the back plate is occupied by two DVI connectors while the other is aerated enough because it has to vent all the hot air pushed through all the copper on the board by the turbine.