Information about the X550 has also been found in ATI's latest Catalyst driver, 5.6, verifying that it's a genuine ATI product.
The X550 is essentially a higher-clocked X300. It's based on the same core as the older chip, the RV370, with four pixel pipelines, a pair of vertex engines and a 128-bit memory interface. While the X300 is clocked at 325MHz, the X550 comes in at 400MHz. That ups the fill rate from 1.3bn texels per second to 1.6bn.
Hong Kong's HIS has also announced an X550-based board, the HIS X550 iFan, again with 128MB of on-board DDR SDRAM, clocked to 500MHz and operating across a 128-bit bus. HyperMemory expands the total memory available to the GPU to 256MB. The maximum supported resolution is 2048 x 1536.