If the number of IO ports of a design is small, the the padframe would be typically small in area or perimeter. Now, if the design's perimeter was larger than the padframe's perimeter, this would be termed core limited. Core limited IO pads are "fatter" or wider than IO limited pads.
If the number of IO ports of a design is large, then the padframe's perimeter would be large and should the design's perimeter be smaller, then this would be a case of IO limited.
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