Is sun rotating around world or is world rotating around sun ?

It depends actually. Where did you define your origin ? Assume that I defined origin of universe as myself my position will be (0,0,0). So any rotation transformation will not change my position. It means all of the other object will turn around myself. Ofcourse it is intuitive to chose sun as origin in first sense , but it is not necessary , same transformations could be applied without chosing sun as an origin. There could be some standart system , than we can represent any position in universe by 3 coordinates. We can easily calculate using its distance and angle. That is actually what OPENGL is doing

Self Compacting DRAM:

Memory compaction is very expensive process. It is required to done in hardware. This case we can have assembly instruction that removes specified area in the memory. Than rest of the parts need to be shifted to empty portion. This requires shift by n circuit. If shift by n circuit could be done in cheap and fast way , we will not need any segmentation and page frames etc.