Computer hard drive is called the primary storage device inside your computer system. You can store a lot of information depending on its capacity to store. It is also where the Operating System installed and loaded when you boot your computer.
If you have low hard disk space in your computer, you do not need to delete some of your files just to free some spaces and that will be the time that you need to buy and install a new hard drive for additional storage of your files.
Purchasing a hard drive for your computer is also critical. You could possibly buy a hard drive which is not compatible with your computer, do not satisfy the storage capacity that you need and its speed in reading and writing your data.
Image Source: www.nkcsystems.com/content/harddrive.jpg Your Hard Drive Should Be Compatible With Your Computer Some motherboards support only one type of hard drive and have only one type of connection for a specific hard drive, this type of hard drive maybe ATA or SATA. You should check very well your hard drive connections from your motherboard before buying a new hard drive.
Image Source: ata http://www.novell.com/coolsolutions/img/16837_hard-disk.gif ATA CONNECTION 
http://www.technoa.co.kr/notes/latestnews/2002/12/16/h/04_s.jpg SATA CONNECTION Hard drives have different sizes, this is because there are different sizes of computer case, choose the best size of your hard drive that will surely fit inside your computer casing. If your computer is small form computer or all in one, you need to purchase a smaller size that will fit for your computer. Ask the vendor about the hard drive sizes, because in worst situation, you might purchase a small size but for notebook hard drives.
Your Hard Drive Should Have Enough Storage Capacity Before purchasing a hard drive, always ask yourself if how much space do you need? You should buy a hard drive depending on your budget, but it's better to consider your maximum budget for your hard drive because the more expensive it is, the more storage capacity it has. The advancement of technology makes hard drive storage capacity larger ranging from 100GB to 1TB. Just buy for a high storage capacity drive because you will need those later on.
Your Hard Drive Should Have Enough Speed Hard drive speed is measure by its "rpm" or revolutions per minute. This is the speed of the spinning platter inside the hard drive. The main functions of hard drive are to read and write data. The read means opening a file, running an application or turning on your computer to load your operating system. The write means saving a new file and installing new programs or applications. This means that the higher the spin rate, the faster to read and write data.
5400 rpm hard drives are mostly installed in notebook computers. 7200 rpm hard drives are found on desktop computers and some hard drives can be as fast as 9600 rpm, these are usually used in server computers. Naturally, the faster the hard drive the more expensive it is. So, buy a hard drive that will fit into your maximum budget.
Always make sure that you should consider these three factors before buying a hard drive. This will ensure you that you will purchase the right drive for your computer and at the same time saving money by purchasing the good one.