TechPowerUp found out some review samples of AMD's new ATI Radeon HD 4830 graphics cards have 560 shaders instead of the advertised 640 shader processors. The site believes some of these slower cards may end up in the retail channel.
The RV770LE graphics processor (GPU) is a "lite" version of the RV770 GPU that went into making the Radeon HD 4850. Out of the 800 stream processors (SP) the RV770 has, AMD carved out the new GPU by disabling two blocks of 80 SPs each, resulting in a 640 SP-laden Radeon HD 4830. Earlier, GPU makers would simply make a BIOS edit that disabled blocks of shader units. Both NVIDIA and AMD these days, resort to physically modifying the GPU, making irreversible changes to the amount of SPs available for the GPU to use. On the sample TechPowerUp got from AMD, there were three such blocks (perhaps accidentally) disabled, crippling the SP count further down to 560.
This did reflect in the card's performance against the one PowerColor sent based on the same GPU. The card from PowerColor outperformed the reference card due to its "proper" stream processor count. We urge reviewers and enthusiasts to verify the stream processor counts of their Radeon HD 4830 samples or products using the aforementioned build of GPU-Z.
More details about the issue can be read over here.