As the CAP and TPI are increasing quickly, pc users get hard drives of bigger and bigger capacity, each platter can hold much more than before.
WD20EFAX-xxFB5Nx 2TB, 1 platter 2 heads
WD30EFAX-xxJH4Nx 3TB, 2 platters 3 heads
WD40EFAX-xxJH4Nx 4TB , 2 platters 4 heads
WD40EMAZ-xxTKPBx 4TB, 2 platters 4 heads
WD60EMAZ-xxTKPBx 6TB, 3 platters 6 heads
WD60EFAX-xxSHWNx 6TB, 3 platters 6 heads