ATI SIMPLY didn’t have enough time to remove the necessity for the master—slave card concept in R520 and the other R5xx cards. We learned that a handful of R520 master cards should be available at launch date and that customers will get them a few weeks after the launch.
ATI’s next generation part, codenamed the R580, will still need a master card concept. ATI realised that due to the picture quality, you need the master—slave card concept just as you need an additional chip on the special card called the “master card” [No relation, Ed.].
Master Card Requirement to Stay in R5xx Series
Source: The Inquirer
The Inq believes that the upcoming R520 will still require the use of a master graphics card and won’t be able to sell just a single GPU as NVIDIA is doing.