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 drive performance.

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 drives.

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.