Pulled these numbers off a spec sheet for a Seagate 750GB Perpendicular Recording drive.

# Number of Discs (physical) 4
# Number of Heads (physical) 8
# Bytes Per Sector 512
# Areal Density (Mbits/sq in) 128,200 Mbits/square inch
# Track Density (TPI) 145,000 tracks/inch
# Recording Density (BPI, max) 926,000 bits/inch
# Recording Components
# Recording Method Perpendicular

I don't remember what the Areal density of the older drives are off-hand.