Intel Xeon D 1521 's Advantages
Released 4 years and 7 months late
Higher specification of memory (4 vs 3)
More modern manufacturing process (14nm vs 32nm)
Lower TDP (45W vs 80W)
Intel Xeon E3 1220 's Advantages
Higher base frequency (3.1GHz vs 2.4GHz)
Larger L3 cache size (8MB vs 1.5MB)