Introduction

• The hard drive in a computer is the component that holds all the data. Documents, programs and even the operating system are stored on the hard drive. Most hard drives are internal; they sit inside the computer tower. There are also external hard drives that are becoming increasingly more popular.
  The external hard drive is located in its own case outside the computer tower. A cooling fan accompanies the hard drive in the case to eliminate overheating. The hard drive connects to and communicates with the computer through a high-speed interface cable. USB and firewire cables are the two most common types of interface cables.
  
  

Why are they necessary?

• People prefer to keep an external hard drive as a backup because of the increased security threats and because they need additional storage space. With new Trojan horses, spyware and viruses popping up every minute, it is becoming very difficult for anti-virus software to keep up with them all. An external hard drive can store backup information in the risk of the primary hard drive being compromised or corrupted.
  Additionally, people are doing more with multimedia files on their computers. Such files can be quite large in size. Having an extra hard drive helps with storing large audio and video collections without overloading the primary hard drive.
  
  

How do they work?

• An external hard drive acts as a plug 'n' play device. It is easy to install and uninstall from the system. The inside of the external hard drive is just like an internal one. There are magnetic platters that hold the data. Controller heads and an actuator arm are used to access the data and to store it on the magnetic platters. The controller controls all of the processes in the hard drive.
  The interface cable is used to communicate with the external hard drive. When the external hard drive needs to be accessed, the request is sent through the interface cable and is accepted by the controller card. The controller card is then checks its registry to see where the data is stored (if data needs to be retrieved) or if there is space available (if data needs to be stored). Once this information has been access by the controller card, it then aligns up the right head with the actuator arm so that it can retrieve data from or store data on the head. The motor in the hard drives spins the head so that the read/write process can be done. Once all of this is done, the data (or a success message) is sent to the operating machine so that the process finishes successfully.