Charlie Demerjian claims uncertainty about whether TSMC will be able to deliver its 28nm HKMG process on time has urged AMD to change its graphics card strategy. Originally, the plan was to launch "Northern Islands" on the 28nm process in 2011, but according to Dermjian the new plan is to launch a second wave of "Southern Islands" graphics cards this Fall. These new GPUs will still be made on the 40nm process and are expected to be some kind of hybrid of the Evergreen and Northern Islands architecture.
To call companies skeptical of the new roadmap is being overly kind. No one believed it, but what can they do? Easy, put plan C into place, and for ATI, that is called Southern Islands.
Southern Islands (SI) is a 40nm family, and from early information, it looks to be a hybrid between Evergreen and Northern Islands. The architectural details are quite slim now, but it looks like ATI took the uncore from NI and put the shaders from Evergreen on it. Think of it as taking the parts that were done and available, and putting them together.
Because it is the only option at this point, SI will be built on TSMC's 40nm process. This is good because it is known, and ready, pulling in the timetables. Low risk means low chance of problems and quick time to market. Expect SI sometime this fall. Rumors abound that some family members have already taped out, but that is far from confirmed.