Hard disk drives (HDD) commonly known as hard disks or hard drives are one of the worst computer components to break down. They can be a real pain when they fail for several reasons. Not only do you stand to lose all of your valuable data, your computer will be unable to operate without a primary hard disk installed.
Fortunately, a hard disk drive is one of the more simple computer components to change though it is important to select the correct type or you will struggle.
Firstly, there are three main forms of hard disk drives. This is an internal 3.5″ drive used on standard desktop computers, a 2.5″ hard disk that is used on notebook and laptop computers and external drives, usually connected by USB, and almost always not a primary drive.
I would suggest that should you be in the situation that your laptop or notebook drive has failed then you seek advice from the manufacturer as to which hard drives are compatible and how straight forward or difficult it may be to change.
Assuming you have a standard computer then you will need to select a 3.5″ drive but there are more options. On a standard computer you will need to ascertain which type of hard disk you have. The two main options are PATA (Parallel ATA) and SATA (Serial ATA). SATA is the newest type of hard drive about at the moment, so assuming your PC is a number of years old it is a pretty safe bet to assume you have PATA.
SATA can be identified in several ways but as you are removing the hard disk anyway you can easily tell by 
the type of connections to the hard drive. PATA has the typical 4 pin connection found on standard CD ROM drives and DVD ROM drives, likewise PATA uses an IDE cable which is about 2 inches in length and is the same type of cable that also connects standard CD ROM drives. SATA has two much smaller connections – about a third of the size.
Apart from the options I have mentioned you have further desicions to make, these decisions will not stop it from working but increase or decrease preformance. These include hard disk speed – faster the better, and capacity, this is the amount of space you physically need as storage. Generally the average computer user will not even use 20% of the smallest capacity hard drives on the market today.
