X-bit labs

First in DirectX 10.1: ATI Radeon HD 3850/3870 (page 6)

Category: Video

by Alexey Stepin , Yaroslav Lyssenko, Anton Shilov

[ 01/25/2008 | 10:31 AM ]

Memory Controller

AMD says the memory controller of the RV670 GPU has been improved to make more efficient use of the available memory bandwidth. The new chip is supposed to be no worse than the R600 in this respect. However, the width of the external memory bus has been reduced from 512 to 256 bits, and the width of the internal ring buses of the controller has been reduced from 1024 to 512 bits. More subtle changes, if any, are inaccessible for us and we can’t say if the RV670 really has an improved memory controller or the memory subsystem of the R600 is just utilized inefficiently. We are prone to believe the latter idea, however, because the Radeon HD 2900 XT doesn’t have any advantages in real applications from its 512-bit external memory bus with a bandwidth of over 100GB/s.

Anyway, the senior Radeon HD 3800 model is superior to the GeForce 8800 GT in terms of memory bandwidth due to its GDDR4 memory. We’ll see in our tests if this advantage is really called for in real-life applications but the new card has a certain reserve of performance here. The ATI Radeon HD 3850 is also better than the Nvidia GeForce 8800 GT 256MB in this parameter: Nvidia’s card has a memory frequency of 1400MHz, which means a peak bandwidth of 44.8GB/s only. For these cards this parameter is not critical, though, because it is the amount of memory, 256MB that is going to be the main bottleneck in games.

So, the ATI Radeon HD 3870 and 3850 seem to surpass the Nvidia GeForce 8800 GT from a technical standpoint, but Nvidia’s card is not so sensitive to application-specific driver optimizations and is backed up by Nvidia’s The Way It’s Meant to Be Played program. It is also obviously faster at texturing. AMD responds with pricing: the official price of the Radeon HD 3870 is set at $219, of the Radeon HD 3850, at $179, which is $40 and $20 lower than the official prices of the corresponding solutions from Nvidia. This makes the new cards appealing if they are available and provide high enough performance in games.

AMD’s graphics department is also rumored to be planning to cut the price of the Radeon HD 3870 from $219 to $199 and of the ATI Radeon HD 3850 from $199 to $159 in near future.