Within sandy bridge architecture, there are total 123 CPUs, 51 desktop and 72 mobile within 10 model ranges, but there are only 3 die sizes the 131mm², 149mm² and 216mm². Which means they are making dual cores natively but probably only highest CPU for dual core and quad core line and the rest are defective and downgraded ones. Only desktop i3 and i7 are being made natively, the i3 is on both 131 and 149 and i7 on 216mm² die.
The desktop i5 and mobile quad core i7 are made from desktop i7 node, the mobile i5, mobile dual core i7, mobile i3, i5-2390T and both desktop and mobile celerons and pentiums are made from both of desktop i3 nodes.