Without hard drives, the modern computer would
be worthless. Hard Drives are used to store data to be used
by the rest of the computer. The advantage a hard drive has
over ram in the computer is data is not lost when a computer
is turned off. Over time as computer programs became larger,
hard drives started to play a bigger role with modern computers.
The first hard drives were created by IBM in 1957 and could
only hold five megabytes. They had fifty magnetic disks and
each magnetic disk was 24 inches in diameter. Current hard
drives vary in size from 3 and half inches in diameter all
the way down to the size of a quarter. The number of magnetic
disks called platters on a hard drive range from two to five.
Over the years, the amount of data that could be put on a
spindle has increased which has allowed hard drives to go
from five megabytes to over 120 megabytes.
Hard drives with just platters are only good for a coaster
for a cup. That is why hard drives also have spindles, controllers,
motor, heads and an actuator all inside a metal casing.
Hard drives are used to store data that is to be used later.
The data could contain data for running a program, an email
from your friends or anything else that you or your computer
will want later. When the data is stored, it is put onto magnetic
platters. When it is time to write the data to the platters
or when the data needs to be read off the platter the controller
on the hard drive tells the heads and actuator what to do
to perform the operation.
When the computer requests data from the hard drive, it sends
the request to the controller on the hard drive. When the
computer wants to send data to the hard drive it again sends
the request to controller on the hard drive. The controller
controls the drive to perform the necessary operation. The
controller's job is to move the heads to where they need to
be and to transfer the data to or from the platters.
When the controller gets an order to perform an operation
one of the first thing it does is speed up the motor if necessary,
however it usually is already spinning since the computer
was first turned on and never turned off. A motor is attached
to the spindle, which spins the platters. Most drive today
spin at 5400 RPM (revolutions per minute), 7200 RPM, 10,000
RPM and a few drives run at 15,000 RPM. Today most hard drives
are considerably faster considering the first hard drives
only spun at 2,000 RPM. While the speed the hard drive spins
in not the only factor in determining how quickly the hard
drive and read or write data, it is a large contributor to
When the motor spins up it also spins up the spindle, which
the platters are attached to. The platters are what hold the
data. The platters are made up of several materials put together.
The core of the platter is most commonly made up of glass
followed by a layer of the nickel followed by chromium. The
next layer is magnetic material, which is nothing more than
very fine iron oxide, which the data is actually stored on.
A very thin layer of carbon overcoat, which is about 15 nanometers,
is on top of the iron oxide. The reason there is a carbon
layer is to increase the mechanical durability of the disk
and slows down corrosion. The last layer that the heads lay
on is made up of a lubricant, which is about 1 nanometer thick.
The more the hard drive is used the more lubricant is removed
by the heads which many times ultimately leads to the death
of the hard drive.
Once the platters are spinning at the correct speed the heads
start moving to the correct place on the platter by the actuator.
A hard drive that has three platters will have six heads.
For each platter, a hard drive will commonly have two heads.
The heads in the hard drive are what reads and writes the
data to the platters. On the tip of each head there is a small
electromagnet that reads and writes that data. Depending on
which brand of hard drive determines exactly how the heads
works. On some drive the heads sit on the platter when not
is use. On other drives, the heads rest on a small carriage
the side of the hard drive. This differences in how a drive
is design and works is based on companies drive design, ideology
and technology. These two different types are referred to
as start-stop drives (CSS) and load-unload (L/U) drives.
Once the heads have read the data the data in then sent to
the buffer on the controller card. A buffer is made up of
solid-state memory. The difference between solid-state memory
and a hard drive is that solid-state memory is faster and
looses data when the power is turned off. When the power is
turned off on a hard drive, it does not loose the data that
has been stored. Most hard drives on the market today have
buffers anywhere from two megabytes to eight megabytes. The
reason for the buffer is that the controller will attempt
to figure out what data the computer will want ahead of time
and will put it in the buffer ready to be sent to the rest
of the computer. The larger the buffer on the hard drive the
better performer the hard drive is. After the data reaches
the buffer it is then passed through the cable plugged into
the hard drive to the motherboard and taken the main system
memory with is several times faster than the fastest hard
The above process is a simplified process of how a hard drive
works. When a hard drive needs to read or write something
the controller receives the request. The controller then controls
the actuator that moves the heads to read the data from the
platters. Once the heads reads the data from the platters,
the data is sent to the buffers. From the buffers the data
is sent to the computer to be processed.