Hard-disk write/read head electronics
Assuming this is a TMR head, I would guess the 6 lines are for: 2 for the write coil, 2 for the the read head, and 2 for a heater. 2 lines are needed for each feature to form a complete electrical circuit.

1st the heater: just like it sounds, it is used to heat up the slider, which is the black box you are referring to. That is a purely mechanical device that controls the aerodynamics of the  head (think airplane wing). Since the disk drive platter can spin pretty fast (5400 rpm ~ 60 mph I think) a lot of windage is created. The slider actually has indentations in the bottom that pull the head towards the platter just like the fins on the front of formula 1 cars pull them down into the race track. Your photo is of the bottom of the slider. Since many materials expand when they heat up, the slider has a coil that can be heated up to make the slider (and attached read/write heads) come a little bit closer to the platter. This is for fine tuning the vertical head position.

2nd the write circuit: there is a simple ferromagnetic material wrapped in a coil to change the direction of magnetization on the end of the slider (on the side facing the loading ramp extension). DC current in 1 direction will cause an up magnetization (for perpendicularly oriented magnetic media), and DC current in the other direction will cause a down magnetization.

3rd the read circuit: by far the most interesting part of the disk drive arm. This also uses a DC voltage that only needs to be oriented in 1 direction. The magnetization on the media will change the orientation of the TMR free layer and the current going back to the preamp along with it. This is how the orientation of the magnetization on the media is detected. The voltage (and thus current) are incredibly small since the signal will pass through a pre-amplifier before being passed back to the disk drive DSP engine (read channel). There is a lot to learn about TMR and would be slightly off topic but I refer you to the following pages if you want to know more:

TMR (disk drive) = http://en.wikipedia.org/wiki/Disk_read-and-write_head#Tunneling_magnetoresistive_.28TMR.29

TMR (theory) = http://en.wikipedia.org/wiki/Magnetic_tunnel_effect

GMR (industry page) = http://www.pcguide.com/ref/hdd/op/heads/techGMR-c.html

Exchange bias = http://en.wikipedia.org/wiki/Exchange_bias

Antiferromagnetism = http://en.wikipedia.org/wiki/Antiferromagnetism

Domain wall pinning = http://en.wikipedia.org/wiki/N%C3%A9el_wall#N.C3.A9el_wall

Great lecture about why pinning works = https://www.google.com/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&amp;cd=2&amp;cad=rja&amp;uact=8&amp;ved=0CCUQFjAB&amp;url=http%3A%2F%2Fneon.mems.cmu.edu%2Frollett%2F27302%2F302.L10.ppt.pin.ppt&amp;ei=MBD-U8fWI8j0iQKSpYDoBw&amp;usg=AFQjCNFBdP1gVrYJVou9vibDg8KZb5gFkQ