A hard drive is an important component of every computer. It is the place where all the information is being stored. Once you lose power, all the data which was residing on the computer will be lost except for data written onto the hard drive. So the hard drive is crucial for keeping all of your data and programs. A hard drive failure is usually catastrophic. Data is usually very hard to retrieve from a hard drive that has crashed. Obviously, I would always recommend making regular backups of your data. Also, you should create an emergency boot DVD which will allow you to put the computer in case of a crash. Without the boot DVD you would have to reinstall the operating system which would override most of the settings of many applications. So therefore it is important to use a hard drive which is from a renowned manufacturer and has high reliability. Even though you might have a backup, it is quite a hassle to restore the contents of the drive.
Hard drives have become smaller. Now many people have swapped to 2.5 inch hard drives. Only hard drives which have very high capacity are usually larger than that. Also, smaller hard drives usually require less power than bigger ones. If you are looking for portability then I recommend getting one of those hard drives. What is important about hard drives is access time. Access time depends how long it usually takes on average to retrieve information. To understand access time, you should understand how data is retrieved from the drive. On the inside of every hard drive is a cylinder which is spinning. The cylinder contains magnetic disks which is store the information. To retrieve information, a mechanical head is moved to the right location. This movement takes a fair amount of time. While accessing one piece of information is still fairly quick, accessing multiple files can get quite time-consuming. That is why it takes a long time to boot your computer. Over time booting the computer becomes even slower because the files on your hard drive become cluttered. That means that the mechanical heads inside the hard drive has to move too many locations during the boot cycle.
Fortunately, they are manufacturers which produce hard drives that are no longer mechanical. These drives use memory chips instead to store information. Obviously, these memory chips are non-volatile which means that even after you turn off your PC, the data is still available. You can also put you operating system on these drives and putting is a lot faster. These drives are called solid-state drives. Read access is much faster than that of traditional mechanical drives. However, the cost per gigabyte of data is higher than that of mechanical drives. Also, it has not yet been tested how often you can actually override information on to one of those drives.