In my Dell is a AMD 64 Athlon X2 4200+ 2,2GHz installed.

But if I take a look at the AMD site for 4200+ I see the ADA4200IAA5CU, ADO4200IAA5CU, ADO4200IAA5DD, ADA4200DAA5CD, ADA4200DAA5BV.

5 processors but wich one is intalled on my stock E521 computer.