Intel Xeon D 1521 's Advantages
Released 6 years and 3 months late
Newer PCIe version (3 vs 2)
More modern manufacturing process (14nm vs 45nm)
Lower TDP (45W vs 130W)
Xeon W5590 's Advantages
Higher specification of memory (1333 vs 4)
Higher base frequency (3.333GHz vs 2.4GHz)
Larger L3 cache size (8MB vs 1.5MB)