Do you remember what an old-time
phonograph(record player, or turntable) looked like?
You had to lift the arm with the
needle to put it at the beginning of the record, or at the beginning
of a particular song, or even in the middle of a song. You could
interrupt a song in mid-stream and lay the arm to rest, you could
set a player to go back to the beginning of the record after the
last song was played and so on.
Now imagine that that the arm of
our record player is controlled externally, by some complex electromagnetic
mechanism, and not by your hand. Imagine also, that the needle
never touches the record, but is very, very close to it. We have
just a few assumptions left. The record is only 3.5” or 2.5” in
diameter and spins very fast – not 45 (or 78 or 33 rpm (revolutions
per minute) like old records, but several thousand rpm!
 What
we just called a record is called a “platter”. That record (platter)
player’s needle is called a “read/write head” or simply “head”.
Now imagine that this contraption
is sealed (almost hermetically) in a small metal box which has
a label on one side and a printed circuit board (PCB) on the other.
There are dozens of parts inside that 
sealed box, which is called
an HDA (Head Disk Assembly).
So, in this crude model, the hard
drive (HDD) consists of two major parts: HDA and PCB.
If you read “How
the PC works", you'll understand how complex a hard drive
is. Now each part of a working drive can fail -- and that's when
it gets really complicated. |
