This spring, AMD has decided to update its top end offer with a new mono-GPU card designed to replace the Radeon HD 4870 and better compete with NVIDIA’s top range cards. NVIDIA, piqued, has reacted straight away with a new GeForce GTX 275 to counter this Radeon HD 4890. Will all this change the situation for gamers?
RV790 vs GT200
The Radeon HD 4890 is based on a new GPU, the RV790, a minor development of the RV770. It is a revision of the RV770 optimised to increase clocks more easily. There is no new function nor any additional processing units and it is still engraved at 55 nanometres. Although the Stream manual does mention a small innovation, this was in fact an editorial error.
This doesn’t however mean that there isn’t a new chip because the RV790 is slightlty bigger than the RV770. We measured them at 16.75x16.75 mm as against 16.50x16.50 mm, which gives a die area of 281 mm² for the RV790 against 272 mm² for the RV770. The reason for this is a a decap ring – or a ring of decoupling capacitors – placed around the chip to reduce signal noise from the different blocks that make up the GPU.
These modifications allow AMD to increase the GPU clock from 750 MHz on the Radeon HD 4870 to 850 Mhz on the Radeon HD 4890, also accompanied by a higher memory clock.
This card posed quite a problem for NVIDIA as the GeForce GTX 260+ that was already jostling for position with the Radeon HD 4870, will not be able to compete with it at all. This left NVIDIA with two options: cut the price of the GeForce GTX 285 or bring out an additional card in its GTX200 range. NVIDIA went for the second solution and is now offering a GeForce GTX 275 based on a GT200 at 55 nm with a simiar configuration to those that equip the GeForce GTX 295.
