The Seagate U Series hard disk Product manual states that the drive has 16 "Default read/write heads" while it has 4/3/2/1 "Physical read/write heads" (depending on actual model). Now, one or two disks is completely normal for a cheap drive 2001.
But what on earth is a "default" head and how can it have 16?
I have never heard of this term. If it refers to -- for example -- the maximum number of addressable heads by the controller logic, then it's a pretty marginal information and why include it among basic and vital information like number of sectors or cylingders? (http://www.codemicro.com/support/disc/manuals/ata/u6pmrevb.pdf, see page 9: Specification summary table)